I was recently reading about football as I often do. For the uninformed reader, my preference is for the collegiate game but I do possess a certain fondness for the professional game. It fascinates me, the extent to which many professionals prepare for and intellectually categorize the intricacies of such a violent game. The machinations of pro football that occur away from the gridiron, on days other than Sunday and during the offseason are intriguing as well. This, notwithstanding the machinations of pro pigskin that I detest.
Anyhow, I was reading Take Your Eyes off the Ball authored by Pat Kerwin. I enjoyed his anatomization of team management activities in the League. In brief, it is a quality read for the novice football fan interested in learning about Xs and Os, team management operations, or both.
In his discussion of special teams play, Kerwin asserts that we “often see a flurry of punts and kickoffs returned for touchdowns [during] the first three weeks of the season.” He attributes this effect to poor management of practice time, roster turnover and the limitations of a 53-man roster, and coverage teams often being comprised of inexperienced players.
I was interested in testing Kerwin’s assertion. Data were culled from the Football Reference Play Finder for seasons 2009-15. I divided the 16-game NFL regular season into quadrants: team-games 1-4, 5-8, and so on, and computed six variables for each quadrant:
- punt return (PR) and kickoff return (KR) TDs;
- PRs and KRs that were not TDs;
- and punts and kickoffs with no return (NR).
| OBSERVED | EXPECTED | ||||||
|---|---|---|---|---|---|---|---|
| GAMES | Kickoffs | KRTD | KR | NR | KRTD | KR | NR |
| 1-4 | 4406 | 18 | 2171 | 2217 | 16.8 | 2489.4 | 1899.8 |
| 5-8 | 4467 | 21 | 2480 | 1966 | 17.0 | 2523.9 | 1926.1 |
| 9-12 | 4382 | 14 | 2620 | 1748 | 16.7 | 2475.9 | 1889.5 |
| 13-16 | 4343 | 14 | 2672 | 1657 | 16.5 | 2453.8 | 1872.6 |
| TOTAL | 17598 | 67 | 9943 | 7588 | |||
Data for KRs and PRs appear in Table 1 and 2, respectively. The values included are the quantities of TDs, returns, and NRs that were observed and those that would be expected given the proportions that emerged. This arrangement is suited for a Chi-square test of independence because that is the analysis we will use. Though excluded for visibility, do note that expected-column totals equal that of observed-columns.
| OBSERVED | EXPECTED | ||||||
|---|---|---|---|---|---|---|---|
| GAMES | Punts | PRTD | PR | NR | PRTD | PR | NR |
| 1-4 | 4137 | 30 | 1833 | 2274 | 24.3 | 1807.9 | 2304.8 |
| 5-8 | 4193 | 19 | 1874 | 2300 | 24.6 | 1832.4 | 2336.0 |
| 9-12 | 4295 | 27 | 1892 | 2376 | 25.2 | 1876.9 | 2392.8 |
| 13-16 | 4233 | 23 | 1768 | 2442 | 24.9 | 1849.8 | 2358.3 |
| TOTAL | 16858 | 99 | 7367 | 9392 | |||
KR TDs are observed more than would be expected during the 1-4 and 5-8 team-games of the season and less than would be expected in the latter quadrants, χ2(6, N = 17,598) = 160.34, p <.001, φC = .067. Given the effect size (φC), we conclude that there is a small but significant disparity in the distribution of KR TDs throughout the season. Although we observed differences in PR TD distributions, the distributional disparities through the season appear minimal, χ2(6, N = 16,858) = 11.98, p = .062, φC = .019. However, it is worth noting that PR TDs during the first four games of the season are probably occurring more than would be expected, supporting Kerwin’s hypothesis.
Chi-square tests indicate that Kerwin is accurate in his assertions. NFL teams surrender more KR and PR TDs early in the season. However, this analysis merely tests the distribution of observed PR/KR TDs and what would be expected to happen given those observations. That is, we are unable to test the influence of poor management of practice time, roster turnover, inexperience, etc. The present analysis does provide a foundation for future studies of the foregoing variables.
