Sunday, September 13, 2015

How Defensive Backs Impact Starting Position via Interception Yardage, or SPI%


The previous post discussed Possessions Responsible for Ending, Possessions Ended, and, focally, Possession Recovered. To accompany that, I planned a metric tentatively termed Starting Position Impact, or SPI. Exactly as the term indicates, SPI is designed to account for a DB’s impact on his team’s average starting field position on offense via his defense of the passing game, currently via interception return yardage but, in the future, ideally, also via pass deflections.

Because drive data is readily available for professional teams, I compiled a data set for all NFL teams from regular seasons 2010-11 through 2014-15. I gathered data for 713 player-seasons in that time period for players who, in a given season, suited up for at least four games and netted at least 1 interception. Players who played for multiple teams within a given season were assigned League average Offensive Drive and Average Drive Starting Position values for that season.

IYPOD is Interception Yards Per Offensive Drives. ADSP is Average Drive Starting Position (on offense).
SPI is calculated simply with the above sequence of equations. Table 1 contains the necessary data for the top-35 DBs in SPI since 2010. The top-35, incidentally, are the DBs who are estimated to have increased their teams’ Starting Position by 2% or greater. That is, without these DBs yardage contributions on INT returns, their teams would have started drives that percentage nearer to their own endzone. 

For perspective, I also included in Table 1 Ed Reed (2004) and Darren Sharper (2009) for reference, the top-2 historically in single season INT yards. Likewise, I included IYPOD estimates for seasons from Deion Sanders, Charlie McNeil, and Night Train Lane. For those three, Team Drives were estimated by summing TDs, FGAs, Punts, game kickoffs, and Offensive TOs, and, for Sanders, failed 4th-down conversion attempts as well.

However, as the regular reader has probably come to realize…I sought a more nuanced and explicatory metric supplementary to SPI. Before I explicate that nuanced metric, however, I will devote the next post to examining how team play on defense and special teams impacts starting field position on offense.



Table 1. Defensive Backs who Increased Their Team's Average Starting Field Position by >2% via INT Yards
Rank PLAYER Tm Year INT Yds Drives Drive Start Yds/Drives SPI%
1 Stevie Brown NYG 2012 307 176 31.4 1.74 5.56
2 Chris Houston DET 2011 225 197 28.7 1.14 3.98
3 Brandon Browner SEA 2011 220 192 33.5 1.15 3.42
4 Janoris Jenkins STL 2012 150 182 24.4 0.82 3.38
5 Ed Reed BAL 2010 183 189 29.8 0.97 3.25
6 Harrison Smith MIN 2014 150 176 27.3 0.85 3.12
7 Kerry Rhodes ARI 2010 174 190 29.7 0.92 3.08
8 Tashaun Gipson CLE 2014 158 193 26.8 0.82 3.05
9 Rashad Johnson ARI 2014 146 181 26.9 0.81 3.00
10 Darrelle Revis NYJ 2011 184 203 30.9 0.91 2.93
11 Ronde Barber TAM 2012 160 193 29.0 0.83 2.86
12 Tashaun Gipson CLE 2013 143 195 26.4 0.73 2.78
13 Charlie Peprah GNB 2011 147 180 30.8 0.82 2.65
14 Chris Harris Jr DEN 2012 144 188 29.1 0.77 2.63
15 Eric Reid SFO 2014 138 175 30.5 0.79 2.59
16 Captain Munnerlyn CAR 2012 107 163 25.5 0.66 2.57
17 Kendrick Lewis KAN 2011 119 189 24.6 0.63 2.56
18 William Gay PIT 2014 113 174 25.7 0.65 2.53
19 Matt Giordano OAK 2011 130 193 27.2 0.67 2.48
20 Brandon Carr DAL 2012 120 180 27.2 0.67 2.45
21 Brandon Boykin PHI 2013 136 201 27.9 0.68 2.43
22 Janoris Jenkins STL 2014 124 186 28.0 0.67 2.38
23 Casey Hayward GNB 2014 113 169 28.5 0.67 2.35
24 Darius Butler IND 2012 101 180 24.8 0.56 2.26
25 A.J. Bouye HOU 2014 120 194 27.7 0.62 2.23
26 Glover Quin DET 2014 117 179 29.9 0.65 2.19
27 Asante Samuel ATL 2012 110 175 29.0 0.63 2.17
28 Patrick Robinson NOR 2012 99 190 24.2 0.52 2.15
29 Tim Jennings CHI 2013 111 182 28.5 0.61 2.14
30 William Moore ATL 2010 117 178 31.1 0.66 2.11
31 Richard Sherman SEA 2013 125 188 31.6 0.66 2.10
32 Malcolm Jenkins NOR 2010 105 174 29.2 0.60 2.07
33 Devin McCourty NWE 2010 110 166 32.1 0.66 2.06
34 Brandon Flowers KAN 2011 95 189 24.6 0.50 2.04
35 Eric Berry KAN 2013 134 197 33.4 0.68 2.04

Ed Reed BAL 2004 358 192 34.2 1.86 5.45

Darren Sharper NOR 2009 376 185 31.4 2.03 6.47

Deion Sanders SFO 1994 303 198 - 1.53 -

Charlie McNiel SDG 1961 349 177 - 1.97 -

Night Train Lane LAR 1952 298 171 - 1.74 -

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