WPA in the ninth
This article from the Sox Watch site has a great insight into scoring WPA for some important, complicated plays.
The final play was a tricky one, and an important one for WPA, because there was a lot on the line at that point, obviously. The Sox WP before the play was 85.4%. Crawford got a base hit to right, scoring Norton, and then Harris threw out Gathright trying to score. On plays like this, I split the action into two separate plays. First, Crawford’s hit scores Norton. If the play had stopped there, we would have had a 5-4 score, with the bases loaded, with a Sox WP of 76.2%. Tavarez therefore takes a -0.092 WPA debit for his role in the play.
From here on, however, Tavarez is not involved in the play, and so all the remaining WPA credit/debit is split among the fielders involved. We start with a WP of 76.2% and the ball in center field, and we finish with Gathright out at the plate, the game over, and a WP of 100%. There is therefore 0.238 of WPA to be distributed. I elected this to split this into three equal parts: One share went to the “Errors” category, which represents errors (and also good plays) by the opposing team. In this case, I consider Gathright’s decision to try for home to be a judgement error.
It’s not clear at this point whether Gathright was waved home or made the call on his own, but in any case, it was a poor decision that helped the Sox. The remaining two-thirds of the credit for this play I split evenly between Harris, who threw a perfectly-located strike to the plate, and Mirabelli, who hauled it in, got set, and made the tag on Gathright.
There is no “correct way” to calculate the WPA of plays like this. But in general, splitting a play into components and logging each one separately is the best way to handle it.