In a previous post I mentioned my intent to explore the effects of defense and special teams on field position. This is part one of that investigation. In another post I offered a method of valuating the average yardage of an interception (for the intercepting team). At present, I will discuss a different method of calculating and valuating INT yards using play-by-play (PBP) data.
Yes, collegiate and professional statistical records include yardage gained on interception returns just as passing or rushing yards are included. However, we track passing and rushing yards as a measure of progress and productivity—a measure of player or team performance. We track interceptions because each signifies an exchange of possession. The interception itself is the measure of player or team capacity—not the yardage gained on returns. Interception return yards are unexpected gratuity.
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| Chris Harris picks off and returns a Kyle Orton pass. |
For instance, consider two interceptions from 2014. A Tony Romo pass was intercepted by NY Giants’ Prince Amukamara and Buffalo Bill Kyle Orton’s pass was intercepted by Dever Bronco Chris Harris. Amukamara and Harris were each credited with 38 INT return yards. Amukamara’s half way through the second quarter of a tie game and Harris’ with 5 minutes remaining in the third quarter, his team leading 21-3. Both players’ offenses scored on their following drives. So what differentiates Amukamara’s INT return from that of Harris? Field position.
Amukamara intercepted Romo’s pass at the NYG 35-yard line and returned the ball to the Dallas 27. Harris intercepted Orton’s pass at the Bronco 2-yard line and returned it to the Bronco 40. Indeed, Harris’ INT may be more valuable because he ended the possession of an opponent in scoring position.[1] But, Amukamara’s 38 INT return yards put his offensive teammates in field goal position before they lined up.
An offense gaining no more than 2.3 yards on every play of every game would be disbanded. A DB intercepting one pass per game and being downed at the spot of each INT would receive a max contract and an eponymous island. No writers would denigrate him for failing to gain yardage after the INT. Any coach or fan would prefer an INT returned to the 50 than one returned to his own 3, of course; but surely every coach or fan would prefer an INT to the opponent having possession.
To me this means that, although there is value in knowing the yardage gained from the spot of an interception to the spot an interceptor is downed, ultimately, it is more meaningful knowing the field position produced by that gained yardage. That is, both players in our example should be credited 38 INT return yards but the values in the game at the point of each player being downed were more accurately described as 73 or 40. This is particularly true if we desire statistics that reflect happenings on the field.
I ran a Pro-Football Reference Game Play search for all interceptions in 2014 regular season excluding pick-sixes and interceptions with lost fumbles on the return. Pick-sixes were excluded because a touchdown precludes an offense driving and, thus, are uninvolved in the tabulation of average starting field position. Four returns with fumbles lost by the interceptor and recovered by the intercepted team were excluded because possession was regained.
Extracted from that data were the (a) spot of the interception and (b) spot of being downed following INT return. Computed with those values were the (c) interception yards from the spot of the INT to the spot of being downed or 20 for touchbacks and (d) starting field position for the interceptor’s offensive unit measured from a team’s goal line to b, the spot of being down. All spot-yardage values were scaled from 1 to 99 with 1 being the intercepting team’s own goal line and 99 being their opponents’ goal lines.
Table 1 contains various interception statistics for 2014 NFL teams, including League averages. The interception return yardage value we are interested in is Mean INT FP column. Teams are ranked by average starting field position following interceptions. Interestingly, I was forced to revisit my earlier debate of the greater value of Amukamara’s and Harris’ interceptions. It appears that over the course of the 2014-‘15 seasons, the Giants’ defense endowed their offense with the greatest field position advantage with interceptions but the average spot of their 16 interceptions was nearly midfield. Compare this to the average spot of the 16 Dallas Cowboys interceptions, their own 30—where opponents are within field goal range. Although intuitive, interception spot increased with field position following interception (N = 393, r = .81, p < .001). Interception return yards also increased with field position following interception (r = .41, p <.001).
| TEAM | Mean FP | Non-TD INT | Mean INT Spot | Non-TD INT Yards | Mean nTD INT Yards | INT FP Yards | Mean INT FP |
|---|---|---|---|---|---|---|---|
| SDG | 26.4 | 6 | 18.8 | 72 | 12.0 | 185 | 30.8 |
| CAR | 27.7 | 10 | 23.4 | 190 | 19.0 | 424 | 42.4 |
| NYJ | 27.8 | 6 | 24.7 | 54 | 9.0 | 202 | 33.7 |
| KAN | 29.3 | 5 | 27.0 | 76 | 15.2 | 211 | 42.2 |
| CHI | 25.9 | 13 | 30.1 | 142 | 10.9 | 533 | 41.0 |
| PIT | 25.7 | 7 | 30.1 | 127 | 18.1 | 338 | 48.3 |
| DAL | 28.9 | 16 | 30.3 | 149 | 9.3 | 634 | 39.6 |
| NWE | 25.5 | 12 | 30.9 | 140 | 11.7 | 511 | 42.6 |
| STL | 28.0 | 10 | 31.3 | 108 | 10.8 | 421 | 42.1 |
| ATL | 26.5 | 15 | 32.1 | 104 | 6.9 | 586 | 39.1 |
| MIA | 31.1 | 11 | 33.1 | 188 | 17.1 | 552 | 50.2 |
| SEA | 27.8 | 21 | 33.5 | 298 | 14.2 | 1001 | 47.7 |
| IND | 28.7 | 11 | 34.5 | 96 | 8.7 | 475 | 43.2 |
| SFO | 30.5 | 11 | 34.6 | 207 | 18.8 | 588 | 53.5 |
| PHI | 30.0 | 9 | 35.3 | 56 | 6.2 | 374 | 41.6 |
| JAX | 25.7 | 5 | 35.8 | 65 | 13.0 | 244 | 48.8 |
| CLE | 26.8 | 18 | 37.9 | 260 | 14.4 | 943 | 52.4 |
| ARI | 26.9 | 15 | 38.3 | 154 | 10.3 | 728 | 48.5 |
| BAL | 28.7 | 10 | 39.1 | 91 | 9.1 | 482 | 48.2 |
| DET | 29.9 | 18 | 39.3 | 336 | 18.7 | 1043 | 57.9 |
| NOR | 30.6 | 16 | 39.3 | 200 | 12.5 | 829 | 51.8 |
| GNB | 28.5 | 15 | 39.5 | 228 | 15.2 | 820 | 54.7 |
| CIN | 30.3 | 19 | 40.4 | 174 | 9.2 | 941 | 49.5 |
| WAS | 25.1 | 6 | 40.5 | 30 | 5.0 | 273 | 45.5 |
| MIN | 27.3 | 11 | 40.8 | 90 | 8.2 | 539 | 49.0 |
| BUF | 30.2 | 18 | 41.2 | 346 | 19.2 | 1088 | 60.4 |
| TEN | 25.8 | 11 | 41.7 | 119 | 10.8 | 578 | 52.5 |
| TAM | 26.6 | 11 | 41.9 | 76 | 6.9 | 537 | 48.8 |
| DEN | 28.9 | 16 | 42.1 | 173 | 10.8 | 846 | 52.9 |
| HOU | 27.7 | 16 | 44.0 | 265 | 16.6 | 969 | 60.6 |
| NYG | 28.2 | 16 | 45.5 | 266 | 16.6 | 994 | 62.1 |
| OAK | 24.2 | 9 | 53.4 | 76 | 8.4 | 557 | 61.9 |
| LEAGUE | 27.9 | 12.3 | 36.8 | 154.9 | 12.6 | 607.7 | 49.5 |
[1] Pro-Football Reference’ Expected Points model tells us that Amukamara’s INT was worth -3.78 EPA and Harris’ -1.6 EPA but Amukamara’s INT yielded a net EP -3.56 and Harris’, -5.91. Amukamara’s INT is worth a greater EPA value probably due to resultant field position but Harris’ INT has a greater net EPA value because his opponent was near the endzone he was defending.
