This study came about from a comment made in passing by Jeff Erikson and Scott Jenstad in a RotoWire podcast. They were discussing how they were worried more about hitters who were striking out on fastballs instead of breaking balls. They figured it was worse to strikeout on fastballs and it showed the hitter was in decline. I don’t remember the exact show but I agreed and now have time verify. And as usual, the pair was right with three-hitter groups differentiating themselves from the pack.
The first key was that I wasn’t interested in the batter ability to tell balls from strikes. Instead, I wanted to focus on pitches right down the heart of the plate while keeping the strike zone as big as possible to increase the sample size. In the end, the taken pitches in the zone used were called strikes 97% of the time.
Next, I found the swinging strike rate for pitches in the strike zone. I grouped the pitches into several groups.
- All fastballs
- Fastballs > 94 mph
- Fastball < 94 mph
- All non-fastball
- All changeups including splitters
- All breaking balls
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