Whether or not longer extra points have affected NFL kickers over the course of the 2015 season has caused much debate. Early-season struggles on both field goals and extra points led many to question whether kickers were worse than ever. However kickers have connected at roughly the same rate as 2014 (thru Week 15). Chuck Zodda discovered that when the data is sliced by field goal distance, an interesting, new trend has emerged.
With Week 15 now in the books, NFL kickers are 726-for-858 on field goals, good for 84.6% on the season. This is nearly identical to the 84.4% they posted through Week 15 in 2014, suggesting no statistically relevant differences. In order to conduct a proper study on field goal accuracy, it is critical to correct for the distance of field goal attempts. Not accounting for distance could skew the results if either longer or shorter kicks occur more frequently.
The table below shows field goal data for the past two years, sliced into 10-yard increments:
|Year||18-29 Yd Makes||18-29 Yd Attempts||30-39 Yd Makes||30-39 Yd Attempts||40-49 Yd Makes||40-49 Yd Attempts||50-59 Yd Makes||50-59 Yd Attempts||60+ Yd Makes||60+ Yd Attempts|
At first glance, the primary difference between the two seasons is an eight percent increase in the number of 40-49 yard attempts, and a fourteen percent decrease in the number of 30-39 yard attempts. There have also been noticeable increases in the number of 50-59 yard and 60+ yard attempts, suggesting that shorter field goals in 2014 are not the cause of the slight bump in overall accuracy.
Much of the data shows little in the way of statistically significant trends, with nearly every slice being within the margin of error expected based on prior year performance.
But the 30-39 yard range does suggest a meaningful change from 2014. Through Week 15 of the 2014 season, kickers went 236-for-267, good for 88.4%. This season, they have gone 213-230 ‒ bumping the accuracy up to 92.6%. A 4.2% increase is statistically significant at this sample size, suggesting with 99% probability that this is a real improvement in accuracy at this distance, as opposed to chance.
Even within this slice, it is important to verify a simple difference in distance is not the root cause. The table to the right has the number of attempts at each distance during the past two seasons:
The average distance of kicks in this range has actually increased slightly from 2014. Thus, the change is not because of a higher number of 31-yarders and lower proportion of 39-yarders.
Given both the increase in accuracy and a slight increase in distance one can safely believe the data suggests there is a meaningful change in kickers’ accuracy at this distance.
The most likely explanation is that the longer extra points have given kickers more opportunities, both in practice and in games, to kick from this distance. Practice does make perfect, and these additional attempts are increasing their comfort and/or ability to repeat their mechanics from similar locations.
This also helps to explain why kickers have been slightly better on extra points than I predicted in the offseason, as the extra repetitions have likely played a role in the improvement there as well.
Follow Chuck on Twitter @ITP_ChuckZ.