What WPA can tell usby Chris Jaffe
June 03, 2013
Wins Probability Added is a fun stat. As THT’s own Dave Studenman likes to point out, it’s the story stat. Designed decades ago, WPA calculates how each event within the game affects the chances of each team winning. It tells us the story of the game: how it feels, where the big moments of drama are. A home run in the ninth inning of a 19-2 game won’t chart at all; that game’s results already have been decided. A home run in the ninth inning of a tie game will have a huge impact, because it will drastically change the odds of a team winning.
Since WPA is designed to chart the ebbs and flows of a game, how the drama rises and falls, I figure that with a large enough sample size of WPA games, you can get a sense of where the drama in a game generally comes from. There are some questions that can be dug away at with a big enough sample size. Thanks to a little bit of digging on my own part, and a really big assist from Eric Johnson, I have a sample size of over 7,000 games to work with: all contests from the 2004, 2011, and 2012 seasons.
How much drama is in a typical game?
The absolute minimum WPA value of a game is 0.500. Both teams start off with a 50 percent chance of winning and each game ends with the victor at 1.000 (a 100 percent chance of victory) and the loser at zero. So if a team scores a ton of runs in the top of the first and then shuts down its opposition, the WPA will be around .500 (1.000 percent minus 0.500). The highest possible one-game WPA is infinite. You can always have another swing in fortune—and the game always can go into extra innings.
So what’s a typical WPA score? Well, the 7,287 games on file have a total WPA of 19,646.965. Thus, an average game should have a WPA value of 2.696, which is about five times the lowest possible score. No game scores the ultimate low of 0.500.
The lowest I have is 0.696, which is exactly 2.000 below the average. That's a neat bit of symmetry there. This value came when the Red Sox torched the Indians, 14-2, on May 25, 2011. Boston scored seven runs in the top of the first to seal it away. Cleveland didn’t score until the eighth, and all their base runners in the first seven innings came with two outs, which dampens the game's WPA score.
While no game is more than 2.000 below the average WPA score, 666 games are at least 2.000 higher, with a mark over 4.696. A game can have an infinite number of twists in it. The highest score is the June 24, 2004, Texas-Seattle contest. The Rangers won, 9-7, in 18 topsy-turvy innings featuring 35 hits, 16 walks, and five double plays. It’s WPA: 9.517. All by itself that compensates for four 0.696 games.
Okay, so if the higher-scoring games can affect the average more than the lower-scoring games can, what’s the median WPA result? Well, the 3,644th best score out of the 7,287 games is 2.497. One game had that score exactly: the Dodgers' 3-1 interleague victory over the Angels on June 23, 2012. If you can’t remember that one, apparently there’s good reason. By WPA, it was a perfectly generic game.
Here’s a chart to show how often you get various WPA scores. Included at the side of the chart is how often you’d see this score per 162 games, to get a sense of how often you’ll see something like this each year:
WPA Score Games Per 162 Up to 1.000 163 4 1.001 to 1.500 815 18 1.501 to 2.000 1249 28 2.001 to 2.500 1425 32 2.501 to 3.000 1173 26 3.001 to 3.500 913 20 3.501 to 4.000 632 14 4.001 to 4.500 599 13 4.501 to 5.000 135 3 5.001 or more 183 4
Before moving on, there’s one other item I want to check on. What are the average scores before digging deeper? You see, Baseball-Reference.com gives each team’s positive and negative scores, what marks they get for each at-bat that helps the team, and the cumulative score for every plate appearance that hurts its chances of winning.
What are the average marks when you dig down? What’s the average positive swing for a winning team and its average losing swing? What’s a typical swing for the losers?
Well, a typical winning team has an average positive good swing of +0.805, and their typical negative swing is –0.560. For losing squads, it’s +0.539 and –0.494.
When you dig into these details, the award for the most generic game of all is a three-way tie. As it happens, all three games featured the White Sox. Their 10-3 win over the Royals on Sept. 17, 2011, a 9-5 loss to the Blue Jays on June 5, 2012, and a 7-5 triumph over Boston on July 17, 2012, had their four components closest to the perfectly average score.
Are games more won or lost?
Since we have such a huge sample size, here’s one question: is the result of a game more due to the victorious team winning it, or is a contest’s result primarily caused by the failures of the losing team? In other words, where do you see the most WPA value pile up, with the winner or loser?
Well, I supposed this shouldn’t come as too much of a surprise, but it’s pretty evenly distributed. As noted above, the games have a WPA total of 19,646.965. Winning teams have a slight majority of that share, though: 50.6 percent (9,946.639) versus 49.4 for the losing team.
Winners pull away a bit more when you go game-by-game. In 3,918 contests—53.8 percent of the total—the score of winners accounts for the majority of the WPA action. That doesn’t include three games where it was perfectly even.
Again, things cluster toward the middle. Over a third of the games have both winner and loser contribute to over 45 percent of the result. Another third has both teams contribute between 40-60 percent of the game’s overall value. Once every 25 games you have a contest where one team is responsible for two-thirds of the overall drama of the game.
The most one-sided game was a 14-3 Padres win over the Marlins in July of 2011. The Padres' WPA value was nearly nine times as high as that of the Marlins. San Diego had positive WPA swings of 0.518 and negative swings of -0.059. Florida barely did anything to impact the game, though: 0.013 positive swings and –0.055. That game was 13-0 by the end of the second inning.
The most extreme case of a team losing was when the Red Sox lost, 2-1, to the Indians on May 3, 2004. Cleveland had very modest WPA swings: +0.264 and –0.370, while Boston had huge marks: +0.999 and –1.605. What happened? Well, Boston kept getting guys on base then not scoring. Since it was a close game, getting guys on caused the Red Sox's WPA scores to rise, only to have them deflate with every snuffed rally. Eight hits and six walks yielded just one run. They had 14 runners left on base, including five at third base and a quartet at second.
Game length and WPA
One way for a game to boost its WPA score is to go into extra innings. Those games typically do better. In fact, the 100 highest-scoring games all went into extra innings. (The best-scoring regulation game? May 17, 2012: Arizona over Colorado, 9-7, with a mark of 6.018 thanks to a flurry of late-inning action).
The average nine-inning game has a WPA score of 2.475, over 0.200 lower than the overall average. 640 extra-inning games have a typical WPA score more than double that: 5.016. It doesn’t take too long for the numbers to really pile up. Here are the averages per inning.
Games Innings Average 1 5 1.426 3 6 1.371 7 7 2.150 8 8 1.881 6628 9 2.475 297 10 4.480 156 11 4.887 88 12 5.544 41 13 6.150 32 14 6.872 13 15+ 7.567Even at 10 innings, WPA values are well above the nine-inning average. The reasons for that are straightforward. Many regulation games are decided well before the ninth, and so there aren’t many points coming out. However in extra-inning games there are always plenty of points racking up. If the game is close in the ninth, even a routine out can change the WPA score by a decent number, especially if there’s a rally on. So the extra-inning games typically have more points through nine and then get to pile even more on after that.
In fact, the lowest-scoring extra-inning game is actually higher than the nine-inning average. On May 28, 2011, the Twins topped the Angels, 1-0, in 10 innings for a WPA of 2.554. That was actually a fantastic game, with the clubs combining for just three hits in the first nine innings, but pitchers' duels don’t register with WPA. It prefers some back-and-forth, not a steady-as-it-goes contest.
This should be a basic one, but let’s check it out anyway. What’s the average WPA score for a game if it’s decided by one run, or two runs, and so on up into double digits?
DIF Games Average 1 2087 3.654 2 1372 2.943 3 1052 2.539 4 892 2.209 5 587 2.002 6 425 1.858 7 299 1.719 8 191 1.600 9 155 1.506 10+ 226 1.420Yeah, that makes sense. The closer the game, the higher the score, just as you’d suspect. What happens if you take out extra-inning games? After all, we just saw that those games have the highest WPA scores, and clearly most of them will have close final scores.
Things change a bit, but the results remain roughly the same:
DIF Games Average 1 1626 3.265 2 1273 2.785 3 1003 2.423 4 873 2.151Here’s another way of looking at it. The average score in a nine-inning game decided by one run is 3.266. Well, games decided by two runs have a score that high just one in every four times. Nine-inning games decided by three runs score 3.266 or high 133 times out of 1,033. Barely one of every 14 games decided by four runs are as good as the average one-run game.
Yeah, that all makes sense if you think about it. And it should make sense, otherwise that means there’s something rather wrong with a stat that’s designed to gauge how the game feels.
Let’s take the above one step further. We know close games are better than blowouts. Shocker. Now let’s ask this: what’s the most exciting final score for a game to have? What’s better, a 3-2 game, a 5-3 tally, or an 11-8 contest?
Well, the games on file have 152 different final scores, from 1-0 to 16-15. But half of those scores appear 10 times or fewer. Only 27 scores appear at least 100 times. Those account for nearly three-fourth of all the games on file. So how do those final scores rank by WPA? Here are the results (the first two columns give the final scores)
RunsW RunsL Games Avg WPA 7 6 156 4.115 6 5 213 3.998 5 4 339 3.940 4 3 371 3.641 3 2 395 3.386 7 5 123 3.306 2 1 309 3.109 6 4 178 3.080 5 3 254 3.020 4 2 293 2.799 1 0 132 2.731 7 4 135 2.727 6 3 183 2.689 3 1 227 2.489 5 2 196 2.487 8 4 101 2.360 7 3 153 2.289 2 0 130 2.222 4 1 223 2.220 6 2 186 2.160 5 1 182 1.958 7 2 114 1.949 3 0 136 1.945 8 2 104 1.884 6 1 152 1.799 4 0 130 1.736 5 0 104 1.572(Random side note: apparently the most common final score is 3-2).
Anyhow, the WPA results makes sense. Closer equals better, and higher-scoring contests have more swings than lower-scoring ones, so the highest-scoring close games are at the top.
What’s interesting is that close generally trumps high-scoring. The top five games listed—and six of the top seven—are all one-run decisions. Even the 1-0 game ranks ahead of any game decided by three runs. I find it interesting that there is virtually no difference between a 2-0 game and a 4-1 contest. Ditto with 7-2 and 3-0 final scores.
In general these results make sense. Then again, they’re supposed to, aren’t they?
References and Resources
All WPA info comes from Baseball-Reference.com. I logged in the 2004 games, and Eric Johnson tallied WPA scores for the 2011-12 games. He normally lists the Game of the Day in the Daily Dugout section at Baseball Think Factory.
History instructor by day, statnerd by night, Chris Jaffe leads one of the most exciting double lives imaginable; with the exception of every other double life possible to imagine. Despite his lack of comic-book-hero-worthiness, Chris enjoys farting around with this stuff. His new book, Evaluating Baseball's Managers is available for order. Chris welcomes responses to his articles via e-mail. Oh, and now he's on twitter.
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