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.
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.
Read the rest of this entry »