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May 122010

J-Doug at Rational Pastime recently noticed that Mariano Rivera’s velocity has been slightly down this April compared to last. He wondered why it was not impacting Mo’s performance, and found two primary explanations (I recommend clicking through to the article to see some nifty velocity and break charts):

Even when Rivera’s cut fastball was coming up short through 8 starts, it certainly wasn’t affecting overall outcomes—Mariano has yet to allow a run this year. Compare this to April 2009 when he had already blown two saves. So why is Mariano still able to compete without the zip on his cutter? Two reasons: break, and luck. While the cut fastball’s velocity is dipping, Mo has added to the already maddening break of his cutter. As you can see in the graph (below), Cut Fastball v.2010 is breaking a full inch more than the 2009 version….

That said, I’m not so sure we can give all the credit to Mo in this case. First off, the strike rate on his cut fastball is down, indicating that the pitch is fundamentally less effective. Second, Rivera’s opponents are only hitting 0.155 against him when they get the ball in play. That’s a full 0.120 below his career average, and 0.230 below where he was this time last year.

I would suggest that the reduced strike rate is probably related to the added break, in that it is more difficult for Mo to be his typically precise self when his cutter is breaking more than usual. As for the overall change in Mariano’s stuff, it is hard to determine what this might mean. His slightly reduced velocity could be a product of his injury, although it is possible that it is simply part of a typical aging process. Mo may be compensating for the loss of velocity by intentionally adding break to the cutter, trying to keep hitters who have more time to adjust to his pitches off balance. I would suspect that as the season continues, his luck will normalize, his velocity will increase, and his strike percentage will stabilize, adding up to more domination from the Yankees ageless closer. I’ll certainly be keeping an eye on the velocity and break on his cutter.

2 Responses to “A Closer Look At Mo”

  1. Rational Pastime is the best new blog to come around in quite a while. I found them a few days ago and have been loving the site.  (Quote)

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