According to ESPN’s sources, 11 of the 12 game balls allotted to New England for Sunday’s AFC Championship Game against the Indianapolis Colts were underinflated by a couple pounds per square inch, failing to meet NFL regulations. This is potentially significant because a flatter football is easier to throw and catch, particularly in the rainy conditions of Sunday’s game.
On its face, this would seem to be a story impenetrable to data analysis. We don’t yet know who or what was responsible for the deflation. It’s also impossible to quantify how much of a boost the Patriots’ passing game received from the flat balls, and although officials detected the underinflated balls at halftime, it’s not clear in which segments of the game the Patriots used the offending balls (for what it’s worth, New England’s highest-scoring quarter came immediately after halftime).
But analytics can at least begin to assess how much of the Patriots’ 38-point victory can be attributed to their passing game.
According to Pro-Football-Reference’s expected points metric, which tracks how many net points are added by each play after accounting for down, distance and field position, Tom Brady and the Patriots’ passing offense added 14.1 points to the team’s margin. By contrast, Andrew Luck and the Colts contributed -10.5 expected points through the air, so the difference between the two teams’ passing production was worth about 24.6 points of scoring margin to the Patriots — still about two touchdowns shy of the Colts’ entire scoreboard deficit.
Now, expected points don’t take into account the leverage of the game situation in which they were produced, so here’s what the game looks like if we break down Pro-Football-Reference’s Win Probability Added (WPA) numbers by play type and quarter:
In terms of game-level WPA, the biggest differences between New England and Indianapolis were in the running game and on special teams, not passing. Also, the Colts’ passing attack piled up more WPA than the Pats did in the game’s first half, when the fullest effect of the deflated balls would presumably have been felt.
Again, we don’t know exactly how much of a boost Brady and company received due to the deflated footballs, but it’s tough to make the statistical case that a moderately reduced Patriots passing game would be enough to close the gap between New England and Indianapolis in other areas of the game. Any deflation effect would have to be much larger to cause that kind of difference.
All of this is probably beside the point, though. Statistically, the Patriots’ videotaping during the Spygate era probably didn’t make much difference either, but the scandal lent an air of illegitimacy to the NFL’s last dynasty. Depending on what the league’s investigation uncovers here, New England could find another unfortunate footnote attached to one of the most impressive 14-year runs in football history.