THE BOOK--Playing The Percentages In Baseball

Wednesday, September 19, 2007

Wow

The future is arriving.  The pinnacle of sabermetrics is the convergence of performance analysis and scouting.  Mariano Rivera is a righthanded pitcher, and for most RHP, they love RHH.  Mo’s splits shows fairly clearly that he loves LHH (OPS of .526 compared to the RHH of .606).  That is, he shows reverse platoon splits.  If you knew nothing about Mariano, you’d have to regress those splits toward the mean of all RHH platoon splits, even though something tells you that you shouldn’t.  But, John Walsh shows us something special: that virtually all of Mariano’s pitches move as if they were thrown by a LH fastball pitcher.  (I think it may be necessary to split his pitch data between LHH, RHH.) Now, all of a sudden, we don’t regress his performance stats to the typical RH pitcher, or the typical RH fastball pitcher, but rather to a RH pitcher who relies almost exclusively on a slider, or on a LH fastball pitcher.  You see, we’ve always been using the hand the pitcher throws with as a proxy for how the pitch moves.  We don’t need to do this any more.  We can actually decide based on how the ball actually moves.

Another thing that I found fascinating was:

The good change-ups that I see tend to dive near the plate, they ‘fall off the table’, as they say. I don’t think they have the vertical movement of a fastball.” Well, you’re right. And me, too—we’re both right. The change does “fall off the table,” but that is thanks to gravity and not to any particular trickery applied by the hurler—the change simply takes longer to get to the plate, allowing gravity to do its handiwork for a bit longer.

Which begs the question as to what the horizontal and vertical movement actually represent in reality.  From the sounds of it, it represents the movement without the effect of gravity (comparing the movement of the ball with spin and no spin).  But, since the time component is of enormous influence here, I submit that it’s silly to use the spin v no spin as the baseline.  Perhaps I’m not understanding something crucial here.

I think the baseline should be one where you choose whatever backspin you want (no spin currently) that forces the ball to travel in a straightline.  That is, the backspin balances out against gravity.  The break of the fastball and changeup is then compared agaisnt this baseline.  If this happens, will it result in vertical breaks that we’d expect?