Adding a new pitch has often been used as an explanation for a breakout year by a pitcher. But with the narrative bias it was important to be skeptical of such claims: when a pitcher adds a pitch and does well we hear about it, when he adds a pitch and nothing happens it is ignored — did you know that Jon Garland added a cutter last year! With the pitchf/x pitch-by-pitch data, we are better equipped to systematically look at the effect of adding a pitch.
Over the past weekend we had the interesting reverse of this story with some suggesting that Kyle Kendrick‘s and Cole Hamels‘, before they pitched very well on Sunday and Tuesday, high ERAs were due to them adding the cutter. It shows how tempting it is to find anything to explain what is almost surely variation from a small sample size. Had Kendrick and Hamels pitched amazingly in their first games everyone would have credited the new pitch. And after both pitched well in their last outings I am sure the narratives will change.
Anyway, the point is that, right now, with both pitchers having thrown less than 20 innings, we cannot possibly assess how the cutter has or will affect the two pitchers. The data does show them throwing the new pitch: Hamels about 14% of the time to the expense of all of his other pitches, and Kendrick over 30% of the time giving up completely on his slider (and it does look to me like the cutter is a distinct pitch and not just a reclassification of the slider). It is just too early to say what this will mean for them (more ground balls? smaller platoon splits? …). But as the season progresses these new-pitch pitchers are interesting to check out because adding a new pitch can have a large effect as Carson, Matt, Mike and I talked about in a recent podcast.