Aging Strikeouts and Height: Extending Corey Hart

The Brewers were talking an extension with Corey Hart, and then they weren’t. Either way, extension is a key word for the 6-foot-6 slugger with the long levers.

The sunglassed-one turns 31 next year, so he’s most likely either post-peak or he’s rapidly approaching his decline phase. At the very least, he’s lost some of the speed he had when he came up as a five-tool player: His speed scores are regularly below average now, and he hasn’t stolen double-digit bases since 2009. His batting profile also has begun to skew more towards power. As it goes with such a move, his strikeout rate has jumped along with his isolated power. How age affects those two talents would be most interesting to his current employer when considering a contract extension.

Height is positively correlated with power. That seems like a no-brainer, and it’s backed up by some limited study on the subject. So maybe it’s not surprising that Hart’s power has remained steady as he’s aged, despite our early findings that isolated slugging might peak in the mid-20s:

Anyone who has watched Hart swing perhaps wouldn’t be surprised that his strikeout rate has risen more than the league’s rate. You get older, your bat slows, and you’ve already got a huge zone to cover. After all:

There’s still a chance this is just a one-person phenomenon, and that he might reverse it with a long off-season of work in the cage. At the very least, he could maintain his current strikeout rates for a while — maybe. Or do tall hitters age worse when it comes to strikeout rates? Jeff Zimmerman helped answer the question by running an [updated] aging curve for hitters in two buckets: shorter than six-foot-two and taller than six-foot-two.

This graph represents the year-to-year change in strikeout rate for position players in three buckets. Jeff Zimmerman uses the delta method to produce his aging curves.

Yikes. Age is not kind to giraffes when it comes to contact rate. And now the tallest players — pitchers — have been removed from the sample, so it’s not all their fault.

Hart has a worse-than average career walk rate (7.1%). His speed has slowly eroded so that it’s below-average. His defense in the corner outfield has consistently been below average. To date, he’s managed to put up good power, along with a passable strikeout rate. Last year, the qualified hitters with an ISO over .235 struck out 21.3% of the time; Hart has spent the past three seasons ISO’ing .235 with a 22.7% strikeout rate. Those are his best traits.

Hart’s post-peak and below average in most phases of the game, but he’s kept his power and strikeout rate acceptable so far. Still, with the strikeout aging curve for tall hitters in mind, extending him becomes a risky venture. You could practically fit an entire Eddie Gaedel in his strike zone, so maybe it’s no surprise.