Do starter or reliever K-rates age faster?

From SABR member Eno Sarris at FanGraphs on January 11, 2012:

When Johnny says his last lines in “The Outsiders” — “Stay gold, Ponyboy. Stay gold.” — there’s more than a slight touch of mortality in the moment. There might even be outright pessimism about the directive. After all, the Robert Frost poem he’s referencing finishes: “Nothing gold can stay.”

Turns out Johnny and Frost know a little something about pitchers and strikeout rates. Thanks to the inestimable Jeff Zimmerman, we have strikeout aging curves for both starters and relievers. As dawn turns to day, it seems, pitchers also lose their gold.


What a stark graph. Zero is the peak, so your average pitcher’s strikeout rate pretty much peaks when he debuts, or shortly afterward. Starters might be able to maintain that peak until 25 years old, or so, but they never really improve the rate. Relievers? Let’s just say you better smoke ‘em while you got ‘em (and then let ‘em walk).

That’s probably the biggest take-away from this graph: If a pitcher’s strikeout rate naturally declines from day one, you probably don’t want to build your team on free-agent pitchers. Despite the high attrition rates for pitching prospects, it seems to make sense that you’d develop your own pitching, rather than aquire — by definition — post-peak free-agents. This also might put a little tiny check mark in Yu Darvish‘s corner, considering the fact that he’s 25 — but that’s a story for another time.

Read the full article here:

Related link: Click here for Tom Tango’s follow-up at “The Book” blog

Originally published: January 12, 2012. Last Updated: January 12, 2012.