A couple of weeks ago, I wrote about a method of calculating a team’s win probability at the end of any given quarter, given the pregame Vegas line and the score margin of the game after the quarter in question. Today, I want to break down those numbers in more detail by looking at which teams (and quarterbacks) added the most Win Probability in each stage of the game.
To compute Win Probability Added (WPA) for the purposes of this post, you look at how much the team’s chances of winning changed from one quarter to the next. For instance, here’s how I’d deconstruct Monday night’s game for the winning Bears:
WPA_loc and WPA_vegas are the two components that make up the pregame win expectancy. Chicago was on the road here, which typically deducts about 8% from a team’s base 50% WP right from the get-go (or roughly 2.5-3.0 points of spread), and on top of that they were 3.5-point underdogs, which put their pregame WP another 2.1% lower than you’d expect from an evenly-matched road team. All told, before the opening kickoff, they were already down about 10% in terms of WP.
Then both teams had a scoreless first quarter, which added 1.3% to Chicago’s total under the WPA_1st banner. This happened because, even though they were still tied, there was less time remaining in the game during which Dallas could exert their theoretical talent advantage (the variance of the future was likely to be higher, which always favors the underdog).
Chicago took a 10-7 lead in the 2nd quarter, which tacked on 13.7% of WP, as seen under WPA_2nd. By this point, they had erased their early 10% deficit and were actually favored to win with a WP of 55.1%. A 14-3 3rd period was the killer, though, adding 42% of WP in the WPA_3rd column. Going into the final quarter with a 24-10 lead, the Bears had a 97.1% chance of winning; when they didn’t relinquish that lead, the remaining 2.9% of WP were added under WPA_4th, since the game was over.
And as is the case with every winning team ever, their WPA_tot for the game was +0.500.
See how it works? By using WPA in this manner, we can detect when in the course of the game a team adds or subtracts the most from its chances of victory. We can also add these WPA numbers up across games at the season level, or even for entire careers.
To demonstrate, here are the leading teams in each type of WPA in a season (including playoffs) since 1978, excluding the strike games of 1987. (Note that all of these tables include *every* team since 1978. I’ve listed 20 teams per table, but you can change that using the drop-down button on the left. All the tables are both sortable and searchable; if you type ‘2012’ into the search box, you can see how the teams this year are doing in the various WPA categories.)
Pregame (Location + Vegas) WPA
1st Quarter WPA
2nd Quarter WPA
3rd Quarter WPA
4th Quarter/Overtime WPA
Last two tables — just for fun, let’s grab the quarterback of note (team leader in dropbacks, i.e. pass attempts + sacks) for each team in every game since ’78, and add up their career WPA by quarter in the games they were the team’s primary passer (including the playoffs, excluding 1987’s strike games):
(“ANYPA-avg” is Adjusted Net Yards Per Attempt above the league average, further adjusted for the strength of the opposing pass defense, home-field advantage, and weather effects in the manner of this old PFR post.)
And here’s that table, but just for playoff games since 1978:
(Note, as usual, that by listing the team’s WPA with its QB of note, I’m crediting the QB with the play of not only the passing game, but also rushing, defense, and special teams, which is clearly too much credit. But people seem to like quarterbacks, QB W-L records, and the like. Hopefully you’ll also check out their ANYPA-avg to see who actually deserves the WPA, and who’s been riding coattails.)
