By Noah Reimers
Every February, the NFL hosts its annual scouting combine. This event welcomes approximately 300 college football players who are looking to take the next step and join the NFL. It has been described as a week-long job interview, complete with personal conversations with teams and on/off-field tests. Without fail, the most anticipated drill each year is the 40-yard dash. As NFL.com explains, this drill is testing a player’s explosion from a static start. Two other drills that are employed at the combine are the vertical and broad jumps. Both of these drills are used to test an athlete’s lower body explosion and power. The shuttle drill is used to test a player’s lateral quickness and explosion in short areas. A similar drill, the 3-cone drill, tests an athlete’s ability to change direction at a high speed. An attendee’s performance at the combine can help their name rise up draft boards. In some instances, bad times can plummet a player’s draft stock. For players who are on the fringe of being drafted, the combine provides a chance for them to either show they belong, or be exposed.
In 2013, Jonathan Bales analyzed the correlation between the 40-yard dash times of running backs and their other drills. His analysis was done on all running backs drafted between 2008 and 2012. He saw that the strongest correlation was between a running back’s 40-yard dash time and their weight (0.51). The second strongest correlation was with a running back’s broad jump (-0.46). Correlation values are from -1 to 0 and 0 to 1. The closer to -1 or 1 the stronger the correlation between the data compared. In this article I will use the absolute value of the correlation values when referring to them in writing.
I set out to find the correlations between all the athletes’ 40-yard dash times and their performances in other drills. I thought that doing so would give me some insight into why times are different between players within position groups. I analyzed all position groups at the NFL combine from 2005 to 2015 and only included the players who participated in all of the drills. The tables below show each position group and what their top three highest correlated drills are with the 40-yard dash (along with the values).
To further the analysis, I attempted to group the positions together by looking at the top correlations for each position. I combined this with some personal football knowledge on what each position does and how it is connected with those around it. I grouped the running backs and wide receivers together because of their low number of highly correlated drills and prevalence of the broad jump. This group will be called the “offensive skill” group. I grouped the cornerbacks, free safeties, and strong safeties together. All three have the broad and vertical jumps as their top two drills, and they are all highly connected on the defensive side of the ball. This group will be called the “defensive skill” group. The guards, tackles, defensive tackles, and centers were grouped together. All four of them have the shuttle or 3-cone correlated with the 40-yard drill at a value of approximately 0.5, which is unique. This group is called “interior” group. The next group was the defensive ends, inside linebackers, outside linebackers, and tight ends. They are called “semi.” All four of these positions had the broad jump and vertical jump in their top 3 and ¾ had both the jumps at or around 0.5. Quarterbacks are left in a group of their own. They are the only position group that had three correlations above 0.52, and they didn’t fit in with any of the other groups. In summation:
- Running backs and wide receivers: Offensive Skill
- Cornerbacks, free safeties, and strong safeties: Defensive Skill
- Guards, Tackles, Defensive Tackles, Centers: Interior
- Defensive Ends, Inside Linebackers, Outside Linebackers, Tight Ends: Semi
- Quarterbacks: Outliers
I then combined the individual position data to create data for each grouping. A scatter plot was created (with the corresponding correlation) for all the correlations that were either the highest, and/or above 0.5 (excluding the quarterback). I separated the data points by whether they were drafted or undrafted to try to display where there may be some sort of cutoff for a player being drafted (or not) based on his combine performance. First for the offensive skill:
The low correlation value with the broad jump for running backs and wide receivers indicates to me that while many of the “offensive skill” players have differing levels of lower body explosiveness, but many can make up for it, or diminish that advantage with foot speed. So while someone might be more explosive, the other player can catch up to their 40 time with stride turnover. While this isn’t a foolproof connection, it could be the link for some of the differences in times within the offensive skill group. Another thing to note is that while the majority of players in the top left portion of the graph (exhibiting a slow 40 time and a low broad jump) went undrafted, there are certainly a lot of outliers, which may point to players who are heavier.
Next for the defensive skill:
This low correlation indicates similar results to the offensive skill. One interesting difference between the offensive and defensive skill is there appears to be a little more spread horizontally (across broad jump results) for the undrafted offensive skill than the undrafted defensive skill. This would indicate that it is easier for an offensive skill player to overcome a poor 40-yard dash with a good broad jump and be drafted. It is worth noting, the major outlier in this group was the Byron Jones, the cornerback from Connecticut, who in 2015 turned in one of the greatest combine performances ever.
The next group plotted is the interior. Here is the plot with broad jump:
The interior group also has a high correlation with the 3-cone drill.
The relatively high correlation value with the broad jump, paired with the relatively high correlation with the 3-cone indicates that players with a high broad jump will likely run a fast 40 for the interior group. More importantly though, the high correlation with the 3-cone may indicate that the times of those players in the interior group are more dependent on the players stride rate than other position groups. The 3-cone in turn is testing an athlete’s turnover of his stride as he changes direction. This also means that some players don’t have to be as explosive in the hips as an interior player to run a fast 40. They could make up for that lack in explosiveness with their stride turnover. For this group there certainly seems to be a cutoff point in measured athleticism when looking at the 40 time and broad jump graph. Above a 5.5 40 and below a 95 inch broad jump could be that point, because few players put up those numbers at the combine and went on to be drafted.
The next group analyzed was the semi:
The semi group also has a high correlation with the vertical jump:
The semi group had both the vertical jump and broad jump highly correlated with the 40-yard dash. This means that the overriding factor in the semi group’s 40 time is their hip explosiveness. The “stride turnover affect” I spoke about above does not seem to be as powerful on these players’ performances in the 40-yard dash.
The last “group” to analyze was the quarterbacks:
The quarterbacks were the true outliers of the position groups. They had both vertical and broad jump as their two highest drills, which wasn’t uncommon, but their values were much higher than the other groups (both above 0.6). This again suggests that the most predictive attribute of a QB for their 40 time is their hip explosiveness. However, the shuttle is their third highest correlated value (0.54), and that indicates that both turnover and explosiveness are highly related to a quarterbacks 40 time. That conclusion for quarterbacks is the most consistent with conventional wisdom about how someone runs a fast 40, and what accounts for differences between players.