With college and professional football swinging into action, now is a good time to look at a study of whether "psychological momentum" carries over from the same team's defense to its offense. For example, if the Chicago Bears' defense thwarts a Green Bay Packers' attempt to go for it on fourth down, does this development spur the Bears' offense to greater immediate success than it would have achieved absent the big defensive play? Presented by Aaron W. Johnson, Alexander J. Stimpson, and Torin K. Clark at last spring's MIT Sloan Sports Analytics Conference, the paper is entitled "Turning the Tide: Big Plays and Psychological Momentum in the NFL." A copy of the paper can be found here.
Johnson and colleagues looked at archival records of nearly one-half million plays from almost 3,000 NFL games between 2000-2010. The way defenses ended their opponents' drives were classified into "big plays" (e.g., fourth-down stops, turnovers due to interception or fumble) or routine stops (forcing the opponent to punt). The authors then asked: Do offenses that take the field as a result of a big play by their defensive teammates do better than offenses who take over after a routine defensive stop?
Three criteria of immediate offensive success were used: number of
yards gained on the first play of the drive, whether the offense gained a
first down (or touchdown) on the drive, and the number of points scored
on the drive.
As I understand the authors' approach, they would find in their vast database, one pair at a time, an offensive drive that began immediately following a big defensive play and another offensive drive that followed a routine defensive stop. The authors made sure, within each contrasting pair, that both drives began from roughly the same yard line, to hold constant field position. Ultimately, a huge number of pairs were analyzed.
What the authors found, contrary to the idea of momentum carryover from defense to offense, is that offensive units that took the field after their defensive teammates had made a big play did not produce significantly more yards, first downs, or points than their counterparts who took the field after a routine stop by their defense.
One question, I feel, that would be interesting to address in future research is whether a big defensive play leads to a team's decision to have the offense go for its own big play upon taking possession (e.g., by throwing a long pass or running a double-reverse). Such a play could come to naught, but if the other team's defense comes onto the field with its heads hanging, the offense could catch the defense off guard.