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.

With a phone full of pictures of pitchers' fingers, strange beers, and his two toddler sons, Eno Sarris can be found at the ballpark or a brewery most days. Read him here, writing about the A's or Giants at The Athletic, or about beer at October. Follow him on Twitter @enosarris if you can handle the sandwiches and inanity.

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10 years ago

I enjoyed that this article was short and to the point, but I would like to understand the graph a little better.

Is it saying the year over year change in K% based on age for each bucket? So to follow this, from 30 to 31 the average 77″ + hitter added 1% to their K rate and starting at 28 they added around 1% per year?

Conversely this is saying that all hitters 76″ and under add virtually nothing to their K% each year?

That doesn’t seem possible that all other hitters are never adding more than 0.2 even once they’ve hit their late 30s.

Anyways…I’m trying to understand this graph, because the way I’m reading it doesn’t make sense to me.

10 years ago
Reply to  odditie

I believe you are reading in correctly. This means Hart may be expected to add 1% a year to his K rate a year, once it gets over 25% look out.

I couldn’t really come up with any examples when thinking of home run hitters except frank howard, who seemed to lower his K rate in some very good years from 30-35. Dave Winfield was the only other player I could come up with that was tall, he also didn’t have a huge increase in K% that I could see, maybe 2-3% over this prime well into his late 30’s. Richie Sexson…I couldn’t think of too many others. Most I thought of ended up being 6’4″ and thus in the middle group.

You said the sample size was over 1000 for those 6’5″ or taller? But how many PAs? If you limit it to players who posted a 175+ ISO before 31, how many players 77″ or taller does that cut? Or even 160+ ISO?

Good article

10 years ago
Reply to  Bill

Is 0.25% really significant? That’d be less than 2 PA per season?

10 years ago
Reply to  Bill

Expanding on this…if a hitter is giving away 0.25% per year starting at 28 they would be giving away around 14 by 35 above what they did at 28.

The 77″+ would be giving away an additional 7 per season or 14 by 30 and around 50 by 35.

So I guess I still think there is something fishy with the graph. It doesn’t make sense that if you are under 77″ tall you basically see no slow down in your bat and if you are over 77″ tall you are dead in the water.