Win Probability Added Leaders Through the LDS

During the postseason, Win Expectancy charts become ubiquitous, because each play, misplay, decision and comeback is magnified in its importance in front of a national TV audience. While Win Expectancy (WE) and Win Probability Added (WPA) aren’t great stats to evaluate players, they are a tool to understand how the dynamics of how a game changes from the first pitch to the last out.

For those not all too familiar with Win Expectancy, our library has a good entry and the interpretation can be boiled down to

If a team is losing and has a 24% win expectancy, only 24% of teams in similar situations in the past have ever come back to win.

So using historical data and the current inning, score, outs and runners on base, WE tells you what percentage of teams have won given those circumstances. These numbers aren’t a prognostication, since anything can still happen, but they give an estimate of what you might expect from the situation.

Win Probability Added is derived from Win Expectancy — being the difference from one play to the next. For example, The batter/runner is given credit for a hit, while the pitcher on the mound will be debited an equal amount for that hit. Plays that dramatically swing the score late in the game with two outs in the inning generally have the highest WPA. WPA is written out like batting average (.000), but it should be interpreted in the same way as win expectancy (0.0%). A play with a .360 WPA increases the WE +36.0%.

Below is our standard WE chart combined with the signed* WPA chart. The WE chart is the running total of the WPA chart. The top chart shows the sum of all the plays until a certain point in the game, and the bottom chart shows the change in WE for each play, which is also the signed WPA.

Top Players

Batters

Now with the basics out of the way, we can make some WPA leaderboards for this postseason. First, batters through the end of the LDS.

This represents the sum of all the at-bats players had from the Wild Card games through the LDS round. Let’s look at Kyle Schwarber to understand why he is near the top of the leaderboard. He’s had 15 plate appearances and three of them have been home runs. Now, Colby Rasmus actually has four home runs this postseason. Even though Rasmus has more home runs, Scwarber’s three home runs affected the WE more at the time they were hit than Rasmus’ home runs did. In fact, Rasmus’ highest WPA play was actually a double. While home runs typically garner the most WPA, Justin Turner tops the chart and didn’t homer once in his 20 plate appearances in the NLDS.

Pitchers

Pitching WPA is a little bit of a different animal since it’s more constant and it depends when the pitcher has come into the game. For example, when a relief pitchers enters with runners on base and no outs then retires the side without giving up a run, his WPA is much larger than if a pitcher started and finished that inning. So there are a few ways to rack up WPA as a pitcher: pitch a lot of low-scoring innings, accomplish the same thing in fewer, but higher leverage situations or by finishing the game, thus removing any uncertainty of losing in a low-scoring game.

We can see those principles play out, as the list is mixed with a combination of starting and relief pitchers. Dallas Keuchel faced 58 batters compared to Jake Diekman, who faced just 19, and they both appear near the top the pitching leaderboard. Keuchel was used both as a starter and a reliever in a low-leverage situation. Since the Royals already had a two-run lead going into the eighth inning, the three-run home run Keuchel gave up to Kendrys Morales didn’t hurt his WPA, even though that home run cemented the Royals’ lead on the way to win the ALDS.

Top Plays

Batters

Looking at WPA on the scale of the individual play, we can find which plays affected the WE the most. For batters most of these are homers and late in the game.

Two plays in Rogers Centre top the list. Hanser Alberto’s single scored the go-ahead run in extra innings and with two outs, and then Bautista’s home run emphatically broke a seventh-inning tie.

Pitchers

The biggest WPA swings for pitchers occur when the inning ends, the score is close and there are runners on base.

Jake Arrieta had the bases loaded with one out in the Wild Card game. The Cubs had a four-run lead, so the WE was only 17.8%, but the difference in the run-scoring potential before Starling Marte’s at-bat and at the end of the double play brought the Pirates WE down to 4.8%. Aaron Loup getting Josh Hamilton to fly out also produced a high WPA, and that’s because it occurred during a tie game in extra innings.

*I use signed WPA because WE charts use a set orientation with regards to teams, and WPA is from the player’s perspective. Signed WPA is WPA multiplied by -1 for events in the top of the inning.