How much of the game is passing, running, kicking, or punting? How much of football are interceptions? Fumbles? How much do penalties impact the outcomes of games? One way to answer that is to simply add up how many of those kinds of plays occurred and divide by the total number of plays. But that’s not going to tell us much, because each kind of play tends to have a different magnitude in terms of its effect on the outcome of games.
When we talk about “how much of football is” something, we need a good definition of what football is. The essence of football, like any other sport, is about competing and winning. So when we ask how much of football is passing, we want to know the impact of passing plays on the outcomes of NFL games compared to other types of plays.
Win Probability can provide the answers. In each game, the WP of each team starts at 0.5, but must end at 1 or 0, for a net total of 0.5 WPA. But between the first kickoff and the final whistle, the WP can swing up and down, traveling far more than the net 0.5. To calculate the total movement, we just need to add up the absolute value (7th grade flashback) of each play’s Win Probability Added (WPA).
Some of the more exciting NFL games feature WP graphs that travel a total of 7 or 8 or more “wins.” In the nearly 2,900 games in my database, there is a total of about 12,000 “wins” worth of total WP travel, for an average of about 4.3 per game. In other words, the WP needle moves, either direction, a total of 4.3 “wins” between the beginning and end of the game.
Now we just need to see how much of that total 12,000 WP movement was due to each type of play. For example, passing plays account for 6,600 of the total WP movement, which equates to 55%. Here are the other play types. (Note that there will be some overlap, so the total will sum above 100%. For example, pass plays also include sacks, penalties, and interceptions.)
|Play Type||% |WPA||
|field goal att||3.5|
We can see why passing has bigger coefficients in the efficiency regression models. It’s more than twice as important in terms of determining game outcomes than running. I was surprised that the % of WP due to penalties wasn’t higher. Often it seems like a few critical flags in high leverage situations can heavily sway a game. Penalty |WPA| does not include plays that featured declined penalties.
Turnovers, both interceptions and fumbles lost, account for 8.4% of game outcomes.
In total, special teams plays—kick offs, punts, and field goal attempts, comprise 11.3% of game outcomes.
Touchdowns plays themselves account for 8.8% of game outcomes. Together with field goals, scoring plays comprise 12.3% of “football.” Most of the other 87.7% doesn’t make the highlight reel.
‘Other’ plays consist of aborted plays, kneel downs, spikes, and plays that could not otherwise be classified.
We can have even more fun with this. Let’s break down |WPA| by quarter.
It’s understandable that the 4th quarter is more determinative than the other three. At first it appears there is something odd with the third quarter, accounting for an unexpectedly low proportion of game outcomes. But it’s actually in line with the other quarters. It's actually the 1st quarter that has a higher |WPA| per play than the 2nd or 3rd quarters. It’s just that teams tend to play at a relatively slow pace in the 3rd quarter. I suppose that’s when teams with leads start slowing down the game. There are also different rules for clock stoppage in the latter quarter of each half.
How about breaking it down by play location? Since 2006 the official NFL play-by-play breaks out seven run locations from left end to right end. It also divides the field into short and deep left, right, and middle for pass plays. Deep is defined as a pass thrown greater than 15 yards in the air from the line of scrimmage.
|up the middle||9.4|
About 81% of all pass attempts are short, so deep attempts are disproportionately determinative of game outcomes, by a factor of about 2 to 1. On a per play basis, the ‘middle’ location for both deep and short passes were both 10% more determinative than the left or right locations at the same depth.
“Up the middle” is far more common than the other run locations. On a per play basis, all the run locations are roughly similar in terms of their impact on winning.
So, unsurprisingly, the NFL is indeed a passing league. In fact, it’s a passing league to the tune of 55%, which is a little more than twice as crucial as running. Penalties don’t control game outcomes as much as I had worried.