FG kicking troubles pervade the college game, frustrating fans, and our conjecturous chat led me to wonder if and how NFL kicking is better than college kicking. This led me to wonder if kickers just get better (or more consistent and reliable) as they get older. We did some Google searching but couldn’t find any NFL kicker aging curves for accuracy. So, we made our own.
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| Figure 1. Histogram of career lengths for NFL kickers 1960-2018 |
First, we obtained a bunch of NFL kicker data from the wonderful resource known as PFR. This includes season-by-season data for 369 NFL kickers from 1960 through present. These kickers made 33558 of 45777 FGs (73.3%) and 54658 of 56369 (97%) extra points. Based on the distribution of career-lengths shown in Figure 1, there were concerns that the large amount of kickers with 3 or fewer NFL seasons would skew the analysis. Our concerns were reinforced when we looked at Figure 2.
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| Figure 2. Mean Field Goal % by length of career in seasons for NFL Kickers 1960-2018 |
Kickers with 3 or fewer NFL seasons have notably lower career FG% than kickers with lengthier careers. This in itself is not surprising, but it would confound the interpretation of the data. The lower accuracy of kickers with 3 or fewer seasons might lead to exaggerated year-to-year increases in accuracy in the early stage of the kicker career. To better convey this, displayed in Figure 3 is the average FG% in each season of the careers of kickers with ≤3 NFL seasons and >3 seasons.
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| Figure 3. Mean FG% in each season for NFL kickers 1960-2018 with career lengths of <4 or >3 seaons |
Figure 3 also suggests that FG% increases linearly as kickers age; as if kickers just keep getting more accurate. However, recall the smaller quantities of kickers with lengthier careers seen in Figure 1. The continued increases in accuracy by kickers with lengthier careers may be obscuring the declining accuracy in later seasons of kickers with shorter careers. This is exactly what is shown in Figure 4.
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| Figure 4. Thick lines are LOESS curves of the average FG% in each season of careers of NFL kickers 1960-2018 with various career lengths; fainter, thinner lines are raw mean FG% in each season |
There is a group of ‘super agers’, kickers with careers longer than 16 years, whose annual FG% seems to level out and remain constant around their 12th season—which is about when kickers with careers of 11-16 seasons begin to experience slight declines in accuracy. Likewise, kickers with 11-16 seasons appear to peak around their 7th season—which is about when kickers with careers of 4-10 seasons start to decline.
Let us look at the data another way. Figure 5 contains average FG% through the course of the career normalized such that 0.50 (on the X-axis) represents a season halfway through the course of the kicker career. Figure 5 shows that, aside from kickers with ≤3 NFL seasons, NFL kickers start to experience a downward trend in accuracy about 75% of the way through their career.
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| Figure 5. Career length is normalized such that 0.00 = rookie season, 1.00 = final season, and 0.50 = halfway through career. Thick lines are LOESS curves of the average FG% in each season of careers of NFL kickers 1960-2018 with various career lengths; fainter, thinner lines are raw mean FG% in each season |
Summarily, the (slightly manipulated) raw data indicate that NFL kickers experience declines in accuracy late in their career (Figure 5). However, using the percent of the way through the career (as in Figure 5) does not conduce toward a prospective aging curve for NFL kickers. That is, a predictive model could not know beforehand how long a kicker’s career will be. In other words, future analyses will need to model an NFL kicker aging curve based on seasons in the League (or perhaps age). Future analyses should also account for era—FG kicking has improved dramatically over the years—and FG accuracy by distance. PAT% might also be informative (more so since 2015). Likewise, some measure of consistency (e.g., coefficient of variation) may provide a more alternative measure (than accuracy) of kicker performance.
