I frequently hear this nugget of wisdom from football analysts: “Team X needs to run the ball to keep Team Y’s high-scoring offense off the field.” At first it makes sense. An offense can’t score if it’s not on the field, no matter how good it is. But at second glance, maybe it’s not so logical.
Number of Possessions
Unlike a sport such as hockey, football is mainly a game based on turns. Football has no face-offs or tip-offs. After one team has possession of the ball, regardless of how that possession ends, the other team will have a turn with possession of the ball. In a pure turn-based game, both teams are going to have an equal number of possessions. But football is complicated by the fact that time expires at the end of each half. In each half it is possible for the team that started the half with the ball to have one more possession than the other. Therefore, in almost all cases the game will end with the number of possessions being equal or within one possession.
I say almost all cases because there are rare exceptions. An interception or punt returned for a touchdown technically does not count as a possession. In those cases, it is possible for a team to have two consecutive possessions. But you don't have to be a statistician to know that's not a good way to get additional possessions. The analysis below accounts for such cases.
I’m not saying that clock management is not important. Once the game clock winds down towards 3 or 4 minutes remaining, it may become somewhat clear how many possessions are likely left for each team. At this point it makes sense to try to manage the clock by play selection and time-outs. And toward the end of a close game it’s absolutely critical.
But until the final minutes of a half, the way the possessions will shake out is completely unpredictable. Until that point, it’s simply silly to try to keep an offense “off the field” by running the ball. Chewing up time by running early in a half does not guarantee your team will be the one with the extra possession. Ironically, a coach may be keeping his own offense off the field for all he knows.
Slowing Down the Game
On the other hand, a strategy that slows down the game could benefit an underdog by causing fewer total possessions by both teams. The more possessions each team has, the more likely it is the better team is going to eventually come out on top. With fewer total possessions, the underdog has a better chance to win because randomness plays a bigger role relative to team ability in a game’s outcome. A 17-10 lead is far more vulnerable than a 34-20 lead to a single kick return or interception return for a TD.
Can Play Selection Really Reduce Possessions?
Can play selection really limit the number of opponent possessions, and if so by how much? Using data from the 2005-2006 seasons, I analyzed how team possessions and time of possession were affected by play selection.
Play selection can be defined multiple ways: run/pass ratio, runs as a percent of total plays, or a simple difference between runs and passes. I chose the simple difference (runs minus passes) because choosing a run excludes a pass. Every choice precludes the other option. A team can’t increase the number of running plays without declining to pass. (It also had the strongest correlation with time of possession (TOP).)
I adjusted the number of offensive possessions by the number of defensive touchdowns allowed. This correction is necessary due to the effect noted above in which a team can actually have two consecutive possessions due to a return for a touchdown. Likewise, opponent possessions were corrected for defensive touchdowns scored.
The correlations between play selection and the other variables are listed below. There are small but significant effects on TOP and team possessions due to play selection.
|Run/Pass Selection Correlation with:||Coefficient|
|Time of Possession||0.23|
|Adj Own Possessions||-0.16|
|Adj Opponent Possessions||-0.15|
The correlation is just as strong for a team’s own number of possessions as for opponent possessions. No surprise here—as we expected, the total number of possessions are reduced but the team choosing to run does not have an advantage.
But how strong is the effect? Is it worthwhile to sacrifice optimum play selection to reduce the number of possessions? Based on the standard deviations and correlations of each variable, we can estimate that for every 3 plays called as a run instead of a pass, a team can expect an average of 1:28 additional TOP.
The correlation between TOP and opponent possessions is 0.08. Therefore on average, a team with an extra 1:28 in TOP can reduce an opponent’s number of possessions by 0.64 drives. Therefore, to reduce an opponent’s number of possessions by a full possession, a team would need to swap about 5 passes for runs.
Teams average 28 run attempts and 35 pass attempts per game. That means a team would need to run about 33 times and pass about 30. Actually, it would probably be closer to 31 runs and 28 passes because of the reduction in remaining game time available.
A team would either need to have a very large advantage in the running game or already have a comfortably large lead to run so much. For even the worst passing teams, passes normally have a much higher expected return than runs. Accounting for the possibility of interceptions, passing still has a significantly bigger expected payoff. Except in specific circumstances such as short yardage situations, for every run play chosen over a pass play, a team is sacrificing some amount of total effectiveness (as long as a team runs often enough to prevent the defense from only defending the pass).
I think a much better strategy for reducing the number of opponent (and total) possessions would be to just tell your receivers and backs to take the hit and stay in bounds a few times. Reducing penalties would have a similar effect by keeping the clock running when it would otherwise stop. That way an underdog can keep the game relatively close by reducing total possessions and still have the freedom to optimize its play calling based on match-ups and game situations.
A coach should play calls to maximize his chances of keeping the ball, getting first downs, and scoring. After all, it’s only incomplete passes that stop the clock. If a coach is calling plays expecting a disproportionate number of incomplete passes, he’s probably going to lose anyway.