Sterling Moore posted a stellar +0.47 +WPA in Sunday's NFC championship game. That's very good -- only Patrick Willis (+0.52) and teammate Dane Fletcher (+0.49) beat that mark for defenders on championship weekend. After all, Moore made arguably the defensive play of the weekend when he knocked what would have been the go-ahead touchdown pass out of Lee Evans's hands with mere seconds to go.
But most of Moore's +WPA actually comes from his contributions on the following play, the failed third down pass targeted for Dennis Pitta which set up the fateful fourth down on which Billy Cundiff kicked the Ravens out of the playoffs. The Ravens were still in excellent shape on that third down, and the failure to convert or score a touchdown took their win probability down from 83% to 43%, giving Moore a +0.40 WPA on the play. That leaves just +0.07 for his other successful play, the strip of Evans in the end zone.
That seems intuitively way too low, and that intuition is correct. Although technically the entire play from snap to throw to almost-catch to strip just cost the Ravens 7% of a win, if Evans holds on to the ball and Moore doesn't strip it, Baltimore's ticket to the Super Bowl is all but punched. But with the way the data is fed into our system, it's impossible to give out separate credit for different aspects of plays.
But let's say for a second it was possible. How would each aspect of that play have played out in the eyes of WPA?
Snap: Second and 1 from the NE 14, 27 seconds remain: 90% win probability.
Things looked great for the Ravens even before this play. With just 14 yards needed for a touchdown and the field goal if they couldn't punch it in just a mere chip shot, the Ravens were sitting pretty. Basically, the only two things which could sink the Ravens were a turnover or the missed field goal.
Throw and catch: Ravens lead 26-23 pending extra point, 22 seconds left: 99% win probability.
It's not over until 0:00, but the Patriots would have needed a Music City Miracle-esque finish to take this one back had Evans held on to the pass for the touchdown. Moore was beat by Evans on the play, but obviously not by much, because...
Strip: Third and 1 from the NE 14, 22 seconds remain: 83% win probability.
Although we can debate how Moore should be credited for this play -- was the throw good enough we don't blame him for less-than-perfect coverage and we merely credit him for the strip, or does the strip just make up for allowing the ball to get to Evans in the first place? Regardless, the actual act of the strip brought the Patriots win probability up from 1% to 17%
So how would I give credit for this play?
Flacco, Evans: +0.09 WPA for the pass and "catch."
Evans: -0.16 WPA for the drop, for a total of -0.07.
Moore: +0.16 +WPA for the strip.
The question of credit is one of the biggest questions those who use and develop statistics for team sports need to answer. Unfortunately, trying to answer these questions in real time makes it almost impossible to give fair answers, and given the subjectivity of certain things, it's almost impossible in retrospect as well.
Keep in mind with the version of WPA presented here, we are only able to give credit based on the entirety of the play. If you see a number that doesn't match up with intuition or common sense, remember the inner workings of an entire play may hold the answer.