Lineman Stationarity
The pocket created by an offensive line is a crucial element of the passing game, as the quarterback needs a clean pocket to throw the ball accurately and on time. A good pocket provides the quarterback ample space and time to move and throw, while a poor one collapses quickly, forcing the quarterback to scramble or take a sack (unless the quarterback is Patrick Mahomes). While it is easy to visualize a good or bad pocket, quantifying its quality, and more generally a lineman's performance, is not straightforward.
This article presents a new metric called "lineman stationarity," which measures the distance that a lineman moves from the ball snap until the next event occurs. Lineman stationarity can be calculated on every offensive play and is useful for evaluating the performance and fatigue of offensive lineman. By tracking the movement and strain experienced by lineman on each play, coaches and analysts can use this metric to gain insights into the overall effectiveness of the offensive line during a game. All metrics and visualizations were generated using data from the 2023 NFL Big Data Bowl.
Lineman stationarity is a measure of how far an offensive lineman moves from their starting position on the field after the ball has been snapped. It is calculated as the difference in yardline position between the moment the ball is snapped and the first event that occurs after the snap. An event, in this context, refers to one of the following:
- the ball is passed
- the quarterback runs the ball
- the quarterback is sacked
- the ball is handed off
- the ball is fumbled
More formally, let Xs be the yardline a lineman is on when the ball is snapped and Xe be the yardline they are on when the next event occurs. Lineman stationarity is defined as Xe−Xs.
Not too complicated, is it? Despite being a simple metric, we'll see that lineman stationarity is very good at evaluating a lineman's performance. In particular, we'll see that higher lineman stationarities are indicative of better team and player outcomes.
Below is an animation of lineman stationarity calculations. The 5 blue dots represent each player on the offensive line, and the brown/red dot is the Football. The length of the yellow lines when the ball is thrown indicate lineman stationarity for each offensive lineman.
On this passing play, the right tackle had the lowest stationarity among the linemen, positioned about -8 yards from his starting position. The center had the highest stationarity at approximately -4.5 yards. It is important to note that lineman stationarity only reflects up and down field movement, as lateral motion is not taken into account. This can be seen in the play when the center moves laterally to help the left guard and tackle, but his stationarity remains low.
Why is Lineman Stationarity a Useful Metric?
Lineman stationarity measures a lineman's ability to hold their ground and provide the quarterback with ample space and time to execute the play. One of the first things we notice about lineman stationarity is that it varies greatly between players who allowed a sack and players who didn't:
We clearly see that lineman stationarity tends to be much lower when sacks are allowed. The Kolmogorov-Smirnov (KS) statistic between these two distributions in the first 8 weeks of the 2021 season was 0.575 with a p-value of 1.05e-95 (essentially 0). This is both statistically significant and a large effect size for the KS statistic.
Moreover, average lineman stationarity varies significantly by other pass results (using the first 8 weeks of 2021 data):
The one-way ANOVA F-statistic for these 5 means was 275.19 with a p-value of 5.27e-234 (essentially 0). From this, we see that average lineman stationarity tends to decrease for worse pass results. That is, completed passes have the highest average lineman stationarity (-3.78 yards), incomplete passes have the second highest average lineman stationarity (-4.13 yards), and so on with sacks and interceptions having the lowest average lineman stationarity.
Another compelling observation about lineman stationarity is that it appears to give insight into lineman fatigue. Consider the following line charts depicting the average lineman stationarity of a team's 5 lineman for each passing play of a game. Vertical red lines indicate plays that a sack occurred.
In all three charts, sacks occur during downward trends in lineman stationarity. For instance, in the first line chart, the offense allowed a sack on the 25th passing play of the game. Prior to the sack, we observe a clear downward trend in average lineman stationarity (we say that lineman stationarity for the current play is in a downward trend if the exponentially weighted rolling average difference in lineman stationarity is negative). Astonishingly, about 85.29% of sacks in weeks 1–8 of the 2021 season occurred when lineman stationarity was in a downward trend. This could indicate that the lineman were fatigued and subsequently giving up more ground on each play, eventually resulting in a sack. Hence, analyzing lineman stationarity for entire offensive lines, as well as individual linemen, could give us a direct metric of stamina, strength, and fatigue.
Another trend appear when we analyze lineman stationarity for an individual player by week, particularly when the player is injured. According to https://www.nfl.com/injuries/league/2021/REG9, Buffalo Bill's guard Jon Feliciano was out during week 9 due to a calf injury. He also missed week 4 due to a concussion. Here's a look at his lineman stationarity for each week that he played:
Following Felciano's concussion and prior to his calf injury, we see a clear negative shift in his lineman stationarity distributions. More concretely, we can see that his highest average lineman stationarity was lower for all the weeks following his concussion than for the weeks prior.
Rankings
Now that we've seen a few reasons why lineman stationarity is a useful metric, let's see which players rank highest in each position. The following plots show the top 10 average lineman stationarities for lineman that played at least 100 passing plays in the first 8 weeks of the 2021 season. Starting with centers:
Then guards:
And tackles:
Many of these lineman are well-known and widely regarded as the best of the best. Others near the top of the lineman stationarity rankings may come as a surprise. This could indicate that lineman stationarity sheds light on unrecognized strengths and weaknesses of each play in the offensive line.
Final Thoughts
In this article, we introduced a new metric called "lineman stationarity" for evaluating the performance of offensive linemen. This metric is based on the idea that a lineman's ability to maintain a stationary position, or remain in place without moving, is an important factor in determining the success of a passing play. We found that lineman stationarity is strongly associated with both the overall performance of the lineman and their level of fatigue. While it is not a perfect metric, it does offer a unique, easily interpretable, and predictive way of assessing the performance of an offensive lineman over time.
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