Buster Posey hasn’t been as disciplined

Buster Posey has had a rough start to the year, but he finally looks like he might be coming out of a year-long, hip-induced funk. He’s hitting .230/.305/.365 which is a downright Tomlinsonian slash line. But things are picking up. He ended a 237 at bat homerless drought on Sunday, and he’s hit two doubles off the top of the center field wall in the last week. The power is returning, and in another month, I’m sure he’ll be rubbing elbows at the top of hitting leaderboards with Christian Yelich and Cody Bellinger and Paul DeJong? That can’t be right.

Posey is starting to look more like himself in terms of power, but there’s still an area where he needs to get back on track and that’s his plate discipline.

Throughout his career, Posey has swung at pitches outside of the strike zone 27.6 percent of the time. We’ve crowned Brandon Belt as the king of the strike zone. Even Duane Kuiper says that Belt knows the strike zone better than umpires. Belt has actually swung at a slightly higher percentage of pitchers out of the zone than Posey.

That’s not the case this year, though. Posey has swung at 36 percent of pitches out of the zone this year. That’s the 16^th greatest year-to-year change in baseball. One of the names above Posey on that list is Gerardo Parra who is up to a 40.4 percent o-swing.

Posey’s fledgling hot streak has happened despite Posey’s o-swing staying the same. Looking at his 5-game rolling average, he’s still swinging at around 35 percent pitches outside the zone.

These stretches aren’t unheard of for Posey and he’ll probably correct himself because he’s very good. What’s a little concerning is that he’s not just swinging at pitches outside the zone but well outside the zone.

Baseball Savant allows us to only look at pitches that are in what’s called the chase zone. That’s indicated by the yellow boxes in the diagram below.

Chase pitches are balls 99 percent of the time and hitters tend not to do anything with them when they do make contact. Unless you’re Pablo Sandoval or Javier Báez, it’s inadvisable to swing at them. In 2019, Posey has swung at 28 percent of chase pitches. Last year, it was 20.9 and the year before it was 17.3.

Posey’s also making less contact on pitches outside the zone. While it’s rare to do anything good with a chase pitch, it’s not impossible. In 2017, Posey slugged .447 on chase pitches likely because he was only swinging at the pitches he knew he could hit. So far, Posey hasn’t had a good result when he’s chased a pitch. His o-contact is 10 percentage points lower than his career average which is driving up his whiff rate. The increased whiff rate is driving up his strikeout rate.

The good news is that all of the above is based on a teeny tiny sample, so this is meant to be descriptive rather than predictive. Just because Posey has been vulnerable against chase pitches doesn’t mean he’ll continue to be.