Key words
sports medicine - NFL - football - NFL combine - NFL combine results - National Football
League
Introduction
The National Football League (NFL) Scouting Combine is an annual event where hundreds
of college football players across the nation gather for physical, medical, and psychological
evaluation [1]
[2]. The combine includes substantial medical testing, with each player receiving an
orthopedic grade that estimates a player’s injury risk [3]. For example, a study examining the combine from 1987 to 2000 showed players receiving
a high orthopedic grade having a mean career length of 42 games, players with a low
orthopedic grade playing 34 games, and players with a failed orthopedic grade playing
19 games [4]. Other studies have shown how injury prior to the combine, among other characteristics,
can help estimate career longevity and how a player’s draft status may be negatively
affected [4]
[5]
[6]
[7]
[8].
In addition to medical testing and orthopedic grade, the standardized physical testing
performed at the combine are objective measures that provide a potential focus for
study [9]. Furthermore, the drills players perform are related to potential injury-reducing
traits, which are physical traits thought to reduce risk of injury, such as ankle
flexibility, proprioceptive ability, proper biomechanics, and jump strength [10]
[11]
[12]
[13]. These are important factors to consider when assessing a player’s risk for injury
that are not directly measured in the orthopedic grading. Performance of athletes
in the standardized physical testing of the NFL combine could offer insight into the
performance and health of players in their future career [14].
Many previous studies have been performed that have sought to find a link between
prior orthopedic injury or NFL combine orthopedic testing results and career outcomes
[3]
[15]
[16]
[17]
[18]
[19]
[20]
[21]. For example one such study found that certain injuries, such as cervical spine
injury, rotator cuff repair, or navicular injury, led to decreased career length when
compared to a control group [3]. However, our study aims to determine the relationship between combine physical
testing and drill performance and career longevity. A study recently established the
relationship between combine physical performance and career longevity for offensive
NFL players, but information regarding defensive players is scarce [7]. To our knowledge, our study is the first to perform an in-depth analysis of original
and normalized combine drill performance and career longevity for defensive NFL players.
We hypothesize better performance in the NFL combine will have a significant association
with career length for all defensive positions.
Methods
Due to the public nature of the NFL combine database and the de-identification of
our results in this study, this study received institutional review board (IRB) approval
and deemed exempt from our institution’s approval board. Our analysis meets the ethical
standards of the Sports Medicine International Open journal [22]. Analysis was completed of all players who competed in the NFL combine from 2005
through 2015. Combine results were retrospectively collected from NFLdraftscout.com,
a public website that provides historical combine results. Results from each drill
that a player had performed at the combine were recorded. These included height in
inches (non-modifiable); weight; BMI (body mass index); 10-, 20-, and 40-yard dash
times; bench press repetitions; vertical jump height in inches; broad jump distance
in inches; short shuttle and 3-cone times. The significance of a player’s performance
on a given combine test can be evaluated by understanding what skills and traits each
drill tests [Table 1]. Career length data were collected using ProFootballReference.com and cross-referenced
using NFL.com team websites from all NFL seasons between 2005–2017.
Table 1 Combine drill descriptions.
|
Test
|
How Test is Performed
|
Significance of Test
|
|
Sprints
|
Performed by running 40 yards from a 3-point stance. Split times recorded at 20 and
10 yards serve as the measurements for the 20- and 10-yard dashes, respectively
|
-
Speed
-
Explosiveness
-
First-step quickness
|
|
3-Cone Drill
|
Performed by a player running around 3 cones that are placed in the shape of an “L.”
|
-
Speed
-
Power
-
Flexibility
-
Agility
|
|
20-yard Shuttle
|
Requires a player to run 5 yards, turn, run back in the opposite direction for 10
yards, and then turn again to run 5 yards back to the starting point.
|
-
Agility
-
Acceleration
-
Power
-
Lateral quickness
-
Coordination
|
|
Vertical Jump
|
Measured using a Vertec device, which the player stands underneath, extends their
arm to mark their maximum extension, and then jumps to hit markers on the Vertec.
The measured difference between standing reach and jumping reach gives a final vertical
jump.
|
|
|
Broad Jump
|
Requires the player to jump outward from a two-foot standing position
|
-
Lower body strength
-
Explosiveness
|
|
Bench Press
|
Players bench press 225 pounds as many times as they can without re-racking the bar
|
-
Upper body strength
-
Endurance
|
The analysis included each player’s combine results and a ratio-scaled normalization
of each player’s combine results by position. Normalizing refers to adjusting a player’s
performance measures by his body size relative to those that he is being compared
against, such as a position group. A ratio scaled normalization, which divides the
player performance numbers by their body mass index, was used for this study. First,
an average BMI was taken for each position. Next, each player’s BMI was divided by
the average for his position in their respective combine year, so that heavier players
would have a higher relative density score. Lastly, combine scores were normalized
for each player by dividing by their scaled BMI, which gave a normalized result for
each test.
The influence of each performance metric on whether or not a player was on a roster
after the combine was evaluated individually using Student’s t-test. Analyses were
conducted in R 3.4.2. All hypotheses tested were two-sided with P<0.05 considered
statistically significant. There was no adjustment for multiple testing.
Our study initially included 10-year roster status in our statistical analysis. However,
due to the lack of NFL players who play ten seasons and subsequent lack of significance,
we excluded the 10-year roster status from our study.
Results
A total of 339 cornerbacks, 356 linebackers, 185 safeties, and 278 inside defensive
linemen were identified from the NFLdraftscout.com database between 2005–2015. Of
these players, 60 cornerbacks, 61 linebackers, 32 safeties, and 46 inside defensive
linemen completed ten NFL seasons and the entire list of combine drills. The 20-yard
dash was not completed by inside defensive linemen and was thus not included in this
study for this specific position.
All defensive positions
A summary of significant results for each position are found in [Table 2]
.
Table 2 Significant combine results by year and position.
|
Position
|
1 Year
|
5 Year
|
|
Cornerback
|
20-yard dash
40-yard dash
Broad Jump
|
Weight
10-yard dash
20-yard dash
40-yard dash
3-cone drill
Shuttle
|
|
Linebacker
|
Weight
10-yard dash
20-yard dash
40-yard dash
Broad jump3-cone-drill
Shuttle
|
10-yard dash
20-yard dash
40-yard dash
3-cone drill
Shuttle
|
|
Safety
|
|
Height
Shuttle
|
|
Inside Defensive Lineman
|
Weight
10-yard dash
Shuttle
|
40-yard dash
Shuttle
|
Physical characteristics (height and weight)
We found no association between height and 1-year roster status. Notwithstanding,
we found an inverse relationship between height and 5-year roster status for safeties,
with shorter safeties being more likely to be on a 5-year roster (72.19 inches vs.
72.83 inches).
We found that higher weight was significantly associated with 1-year status for linebackers
(241.15 vs. 238.25) and inside defensive lineman (306.86 pounds vs. 301.21 pounds).
We found a significant association between weight and cornerback 5-year status (194.20
pounds vs. 191.20 pounds) (
[Table 3]
).
Table 3 Average combine results for physical characteristics (height and weight) of defensive
positions compared to roster status.
|
Physical Characteristics
|
|
Position
|
1 Year
|
5 Year
|
|
Yes
|
No
|
Yes
|
No
|
|
Cornerback
|
Height Mean (sd)
|
71.24 (1.47)
|
70.90 (1.72)
|
71.31 (1.56)
|
71.13 (1.45)
|
|
Weight Mean (sd)
|
193.04 (8.54)
|
192.12 (9.09)
|
194.20*(9.44)
|
191.20 (8.02)
|
|
Linebacker
|
Height Mean (sd)
|
73.59 (1.28)
|
73.43 (1.55)
|
73.59 (1.21)
|
73.40 (1.41)
|
|
Weight Mean (sd)
|
241.15*(8.68)
|
238.25 (9.13)
|
240.46 (7.84)
|
240.00 (9.57)
|
|
Safety
|
Height Mean (sd)
|
72.28 (1.44)
|
72.83 (1.35)
|
72.19*(1.46)
|
72.83 (1.51)
|
|
Weight Mean (sd)
|
208.36 (9.03)
|
208.80 (9.49)
|
208.68 (9.69)
|
208.58 (9.40)
|
|
Inside Defensive Lineman
|
Height Mean (sd)
|
75.06 (1.45)
|
74.90 (1.47)
|
75.05 (1.32)
|
74.85 (1.41)
|
|
Weight Mean (sd)
|
306.86*(16.93)
|
301.21 (15.79)
|
305.63 (15.93)
|
303.39 (15.49)
|
*Denotes statistical significance with a p-value < 0.05.
Speed and first-step quickness (10-, 20-, 40-yard dash)
We found the 10-yard dash was significantly associated with 1-year roster status for
linebackers (1.61 seconds vs. 1.65 seconds) and inside defensive lineman (1.74 seconds
vs. 1.78 seconds). The 10-yard dash was also significantly associated with 5-year
roster status for cornerbacks (1.52 seconds vs. 1.56 seconds) and linebackers (1.60 seconds
vs. 1.62 seconds).
The 20-yard dash was significantly associated with 1-year status for cornerbacks (2.57 seconds
vs. 2.63 seconds) and linebackers (2.69 seconds vs. 2.75 seconds). The 20-yard dash
was also significantly associated with 5-year roster status for cornerbacks (2.55 seconds
vs. 2.63 seconds) and linebackers (2.69 seconds vs. 2.74 seconds).
The 40-yard dash was significantly associated with 1-year status for cornerbacks (4.47 seconds
vs. 4.55 seconds) and linebackers (4.68 seconds vs. 4.82 seconds). The 40-yard dash
was also significantly associated with 5-year roster status for cornerbacks (4.42 seconds,
4.54 seconds), linebackers (4.66 seconds vs. 4.75 seconds), and inside defensive lineman
(5.03 vs. 5.13 seconds) (
[Table 4]
).
Table 4 Average combine results for speed and first-step quickness (10-, 20-, 40-yard dash)
of defensive positions compared to roster status.
|
Speed and First-step Quickness
|
|
Position
|
1 Year
|
5 year
|
|
Yes
|
No
|
Yes
|
No
|
|
Cornerback
|
10-yard dash Mean (sd)
|
1.55 (0.08)
|
1.57 (0.08)
|
1.52*(0.08)
|
1.56 (0.08)
|
|
20-yard dash Mean (sd)
|
2.57*(0.11)
|
2.63 (0.12)
|
2.55*(0.11)
|
2.63 (0.12)
|
|
40-yard dash Mean (sd)
|
4.47*(0.18)
|
4.55 (0.21)
|
4.42*(0.17)
|
4.54 (0.19)
|
|
Linebacker
|
10-yard dash Mean (sd)
|
1.61*(0.07)
|
1.65 (0.07)
|
1.60*(0.07)
|
1.62 (0.08)
|
|
20-yard dash Mean (sd)
|
2.69*(0.10)
|
2.75 (0.18)
|
2.69*(0.10)
|
2.74 (0.12)
|
|
40-yard dash Mean (sd)
|
4.68*(0.17)
|
4.82 (0.17)
|
4.66*(0.16)
|
4.75 (0.18)
|
|
Safety
|
10-yard dash Mean (sd)
|
1.56 (0.08)
|
1.57 (0.07)
|
1.54 (0.09)
|
1.57 (0.08)
|
|
20-yard dash Mean (sd)
|
2.61 (0.12)
|
2.62 (0.12)
|
2.61 (0.14)
|
2.64 (0.11)
|
|
40-yard dash Mean (sd)
|
4.54 (0.20)
|
4.55 (0.20)
|
4.52 (0.21)
|
4.58 (0.20)
|
|
Inside Defensive Lineman
|
10-yard dash Mean (sd)
|
1.74*(0.10)
|
1.78 (0.10)
|
1.72 (0.1)
|
1.75 (0.10)
|
|
40-yard dash Mean (sd)
|
5.06*(0.25)
|
5.18 (0.26)
|
5.03*(0.24)
|
5.13 (0.26)
|
*Denotes statistical significance with a p-value < 0.05.
Explosiveness and power (broad jump)
The broad jump was significantly associated with 1-year status for cornerbacks (122.71
inches vs. 118.98 inches) and linebackers (116.95 inches vs. 114.52 inches) but was
not associated with 5-year roster status for any defensive position (
[Table 5]
).
Table 5 Average combine results for explosiveness and power (broad jump) of defensive positions
compared to roster status.
|
Explosiveness and Power
|
|
Position
|
1 Year
|
5 Year
|
|
Yes
|
No
|
Yes
|
No
|
|
Cornerback
|
Broad Jump Mean (sd)
|
122.71*(7.53)
|
118.98 (7.96)
|
122.28 (7.72)
|
121.60 (8.13)
|
|
Linebacker
|
Broad Jump Mean (sd)
|
116.95*(7.67)
|
114.52 (8.34)
|
116.41 (7.67)
|
114.97 (7.86)
|
|
Safety
|
Broad Jump Mean (sd)
|
120.74 (7.43)
|
121.88 (10.05)
|
120.82 (7.68)
|
120.08 (7.74)
|
|
Inside Defensive Lineman
|
Broad Jump Mean (sd)
|
105.72 (10.69)
|
107.47 (11.36)
|
106.81 (10.13)
|
106.14 (10.96)
|
*Denotes statistical significance with a p-value < 0.05.
Agility (3-cone drill, shuttle)
The 3-cone drill was significantly associated with 1-year roster status for linebackers
(7.13 seconds vs. 7.32 seconds), 5-year roster status for linebackers (7.11 seconds
vs. 7.20 seconds), and 5-year roster status for cornerbacks (6.89 seconds vs. 7.00 seconds)
The shuttle drill was significantly associated with 1-year roster status for linebackers
(4.29 seconds vs. 4.41 seconds) and inside defensive lineman (4.65 seconds vs. 4.74 seconds).
The shuttle drill was also significantly associated with 5-year roster status for
cornerbacks (4.14 vs. 4.23 seconds), linebackers (4.27 vs. 4.34 seconds), safety (4.16
vs 4.26 seconds), and inner defensive lineman (4.62 seconds vs. 4.71 seconds) (
[Table 6]
).
Table 6 Average combine results for agility (3-cone drill and shuttle) of defensive positions
compared to roster status.
|
Agility
|
|
Position
|
1 Year
|
5 Year
|
|
Yes
|
No
|
Yes
|
No
|
|
Cornerback
|
3-Cone Drill Mean (sd)
|
6.93 (0.32)
|
7.02 (0.37)
|
6.89*(0.34)
|
7.00 (0.33)
|
|
Shuttle Mean (sd)
|
4.18 (0.22)
|
4.23 (0.25)
|
4.14*(0.22)
|
4.23 (0.21)
|
|
Linebacker
|
3-Cone Drill Mean (sd)
|
7.13*(0.28)
|
7.32 (0.28)
|
7.11*(0.27)
|
7.20 (0.31)
|
|
Shuttle Mean (sd)
|
4.29*(0.19)
|
4.41 (0.21)
|
4.27*(0.18)
|
4.34 (0.21)
|
|
Safety
|
3-Cone Drill Mean (sd)
|
6.96 (0.31)
|
7.04 (0.33)
|
6.91 (0.37)
|
7.04 (0.27)
|
|
Shuttle Mean (sd)
|
4.21 (0.21)
|
4.26 (0.12)
|
4.16*(0.24)
|
4.26 (0.18)
|
|
Inside Defensive Lineman
|
3-Cone Drill Mean (sd)
|
7.68 (0.38)
|
7.73 (0.35)
|
7.65 (0.38)
|
7.76 (0.37)
|
|
Shuttle Mean (sd)
|
4.65*(0.25)
|
4.74 (0.25)
|
4.62*(0.22)
|
4.71 (0.26)
|
*Denotes statistical significance with a p-value < 0.05.
Discussion
The standardized physical testing performed by players in the NFL combine is utilized
by NFL coaches, teams, and team physicians to measure a player’s athleticism and future
potential [14]. Our study found certain combine drills correlated with longer NFL careers for each
position for defensive players. Out of all the combine tests, the 20-yard dash results
had the highest number of significant associations with 1-year roster status, with
3 of 4 defensive positions yielding significant results. We found a significant association
with the shuttle results and 5-year roster status for all 4 defensive positions. This
was closely followed by the 40-yard dash results, which was significantly associated
with 5-year roster status for 3 of 4 positions. The combine results that were not
significantly associated with 1-year roster status and 5-year roster status were height
and weight, respectively. Whereas other studies have investigated the use of various
combine tests to estimate NFL career success or propensity for injury, our study is
the first to perform an in-depth analysis examining the relationship between standardized
physical testing in the NFL combine and career longevity.
Explosiveness and power is measured in the NFL combine through the vertical and broad
jumps [23]. Our study shows a significant association between broad jump and 1-year roster
status for cornerbacks and linebackers. However, there was no significant association
between the broad jump and 5-year status for any of the studied defensive positions.
Agility is measured through the 3-cone drill and shuttle. The shuttle test had the
most significant findings among the two tests, with faster times significantly associated
with 1-year roster status for linebackers and inside defensive lineman and significantly
associated with 5-year roster status for all positions – cornerbacks, linebackers,
safeties, and inside defensive lineman. The 3-cone drill speed was significantly associated
with 1-year roster status among linebackers and 5-year status among cornerbacks and
linebackers.
Short distance speed and first-step quickness are extrapolated from the 10-, 20- and
40-yard dashes. Faster 10-, 20-, and 40-yard dash times were correlated with increased
likelihood of 1-year and 5-year roster status among linebackers, indicating a significant
association between all linebacker dash times and career longevity. Among a variety
of significant findings, the 40-yard dash was the most valuable test for cornerbacks
and inner defensive lineman, with an increased likelihood of 1-year and 5-year roster
status for both positions. No significant association was found with 10-, 20-, and
40-yard dashes among safeties for 1-year or 5-year roster status, however, this was
likely due to the small sample size of safeties and should be studied further.
A previous study by Berri et al. [24] reported height as having a significant association with career length for certain
positions, such as quarterbacks, however our results demonstrated height was inversely
correlated with career longevity for safeties, with each 0.25-inch increase in height
correlating with a decrease of 7.2% chance of being on the 5-year roster. Height was
not significantly correlated with any defensive position. Inside defensive lineman
and linebackers with higher weights had significantly increased chances of being on
the 1-year roster; however weight had no significant effect on 5-year roster status.
In contrast, we found a significant association with weight and 5-year roster status
for cornerbacks, indicating increased weight among cornerbacks leads to longer career
longevity.
A limitation to our study is the use of online NFL combine results, which are dependent
on accurate data collection and recording. Despite this limitation, the NFL combine
results are widely used in scientific study. Another limitation of our study is the
use of normalized data, which we calculated without allometric adjustments. Although
BMI can be less useful in individuals at the extremes of body mass, such as professional
athletes, we attempted to account for this by normalizing the data and comparing individuals
by position group using a ratio-scaled normalization. A ratio-scaled normalization
refers to normalizing BMI by dividing weight over group BMI, and allosteric normalization
uses specific exponents tailored to the group that is being studied to derive its
normalization. By using a scaled BMI approach in interpreting the data, we feel it
allowed for the most accurate comparison in the absence of a consistent exponent for
allometric adjustments in football players. Allometric adjustments are intended to
provide a more accurate normalization of athletic drill performance by assigning an
exponent value to describe body shape and size rather than simply BMI. Therefore,
allometric adjustments could be useful if an accurate exponent for American football
athletes is developed. Our study also attempts to determine the relationship of combine
results and career longevity for a dynamic sport in which athletes experience an extreme
variance of situations, playing conditions, and more. Although our results are useful
and informative, caution must be taken when applying these results to individual athletes.
Of course, athletes with excellent results could experience catastrophic injuries
and shortened careers, and athletes with below-average results could have lengthy
careers. Further, injury mechanism was not accounted for when considering career length
variance,
The NFL combine is used to evaluate football players. Although the combine is useful
to help NFL teams gather medical histories, perform physical exams, and perform athletic
tests to filter through and recruit the most promising players, our study demonstrates
the utility of the combine physical testing results for estimating career longevity
for defensive players. This study can be used by NFL teams, team physicians, and other
healthcare professionals to assist in the assessment and treatment of NFL defensive
players. Future studies should examine whether the NFL combine results could be used
in other areas of sports medicine, such as injury prevention.
