## FanGraphs Pitch Framing

In 2008, when Dan Turkenkopf was the first to quantify the value of pitch framing, he noted that it appeared to be alarmingly important. Bill Letson was similarly astounded when he calculated the size of the effect in 2010. Max Marchi and Mike Fast each took a turn in 2011, finding large and highly correlated catcher values despite using different methods. Other sabermetric luminaries have contributed sophisticated methods and sanity checks, some of which I’ll touch on below. And yet, this terrifically important, seemingly well-established, and impressively repeatable defensive skill has been left out when calculating FanGraphs player WAR and ignored when Steamer forecasts pitchers and catchers. . . until now.

In what follows, I’ll briefly lay out a series of steps for calculating how many framing runs each catcher contributed as well as and how many extra strikes each pitcher was granted (or, in some cases, earned). This much has all been done and clearly described before thanks to Dan Brooks and Harry Pavlidis; that research was updated and expanded upon by Pavlidis and Jonathan Judge. I’ll then compare the values I’ve obtained to the ones created by Baseball Prospectus, StatCorner, and Sports Info Solutions and demonstrate (I hope) that those extra strikes really do result in extra strikeouts and fewer walks. Lastly, I’ll discuss what this means for Steamer forecasts.

### Modeling the Strike Zone

It all starts with the strike zone and I started by using generalized additive models to estimate the probability of a strike in any count, to either left-handed or right-handed batters at each location in and around the plate. On the first pass (shown below), I created strike zones averaged across seasons and, on the second pass, looked for changes in the strike zone by season. The blue contour lines in the images below show where strike calls are a coin flip and the red dashed lines show where we’d expect a 25% or 75% chance of a strike. If you’re read Matt Carruth or Jon Roegele, you’ll be unsurprised to see a small 0-2 strike zones (shown in the upper right facets) and large 3-0 strike zones (in the lower left).