Why Are Hitters Swinging At More Bad Pitches?

Today, instead of telling a story using numbers, I’ll let the numbers do all the storytelling. I think in this case that they have something to say. The table below comes from Jamie Moyer’s plate discipline stats. While I am interested in Moyer in general, it’s not his stats here that jumped out at me. Instead it’s the major league averages, which appear in the orange-colored rows.

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The first two columns certainly stand out. While overall swing percentage isn’t too far off from previous years, both O-Swing% and Z-Swing% have moved moved a bit. This year hitters are swinging at 28 percent of pitches outside the zone, a nearly three point jump from 2009. The number does move around a bit, dipping as low as 16.6 percent in 2004. On the other side, hitters are swinging at fewer pitches inside the zone as last year, 63.8 percent against 66 percent from last year. That number appears to increase to some degree all the way back to 2002. We’re also seeing much more contact on pitches outside the zone.

I’m obviously wondering why we’re seeing this discrepancy. Why are hitters swinging at pitches outside the zone more frequently than in the past? This seems like a good question to crowdsource. I’ll present a couple of ideas, and you guys can build on them. It’s certainly something I’d like to hear more about.

1, This is just an early season thing. They say hitters get better as the weather warms. Maybe that has as much to do with them getting into a groove — hitters are getting closer to the 250 PA mark — as it does the weather.

2. It’s just part of the natural cycles of the game. Hitters were more patient earlier in the decade. Maybe now they’re starting to be more aggressive.

3. Related to No. 2, and perhaps a bit to No. 4, pitchers are exploiting a weakness and are making hitters chase more.

4. Pitchers are just hurling nastier stuff. Hitters are having a hard time adjusting to tougher breaking and off-speed pitches. I’m not sure how you could go about proving this one, so it’s probably an afterthought, if that.

5. The criteria for pitches inside and outside the zone has changed.

6. Just blame the umps.

Again, I’m not really sure if this is something that we’ll see continue all season, or if No. 1 more fully explains it. I’m also sure that there are many, many more possible reasons. I’d like to hear them, though.