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A Ronald Belisario scouting report

Beware, worms!

Jeff Curry-USA TODAY Sports

Yesterday, one day before he would have opted out of his minor league contract, the Tampa Bay Rays promoted reliever Ronald Belisario to the major league team. Belisario has been a very good pitcher in the past, highlighted by 2012, when he put up a 2.54 ERA with a 24% strikeout rate, a 10% walk rate, and a 65% groundball rate.

In the two years since then, Belisario has put up much less impressive 16% strikeout rates, and his 2014 campaign featured a bloated 5.56 ERA, but fielding independent pitching metrics like FIP and xFIP still liked him, thinking he deserved a ERA closer to the 3.50 range.

Moreover, while it would be foolish to expect many strikeouts from Belisario based on his record, there is one thing you can count on: lots of ground balls. Groundballs are generally a good thing for pitchers, and they're more of a good thing for pitchers who get lots of them.

Think of it this way. If a pitcher produces a ground ball 60% of the time, that means that batters are consistently swinging over his pitches. If batters consistently swing over it, chances are that they're swinging over it by a greater amount than they would against a more normal pitcher. And if they're swinging over the ball by a greater amount, the contact is less square, and the ground balls are hit less hard.

That's the rational for why systems like SIERA improve their accuracy by expecting lower than normal batting averages on balls in play for pitchers with either extreme grounball and extreme flyball tendencies.

So how does Belisario reach this extreme? Here are his pitches from last year.

The biggest reason is his sinker. I use the terms "sinker" and "two-seam fastball" interchangeably to mean whichever version of a pitcher's fastball has less vertical rise and more horizontal run, but Belisario's is the type of fastball that deserves to be called a sinker. It comes in on the hands of a righty and away from a lefty at 95 mph with around ten inches of run, and while the average sinker from Belisario rises about three inches due to it's spin, he occasionally gets it to actually drop due to spin. That's extremely rare for a fastball.

Interestingly, Belisario doesn't appear to have consistently pounded the bottom of the zone over his career, more often working through the vertical center of the zone, inside to righties and away from lefties. When his sinker is put in play, it's been a groundball 68% of the time.

Belisario's most-used secondary pitch is a hard 87 mph slider, that really has motion more like a cut fastball. It's drop is average for a slider, but it's horizontal motion is well below average. Sliders tend to be good strikeout pitches, rather than groundball producers, and Belisario's is about average at creating whiffs (on 33% of swings), but is well below average at producing groundballs (37% of balls in plays).

I'm not sure Belisario's slider is very good, and I wonder if the Rays will have him de-emphasize the offering slightly. That's because his third pitch, a changeup with splitter-ish movement, appears to be underused.

Belisario has only thrown 125 changeups in his career, with the majority of those coming over the past several years. His is a hard changeup at 88 mph, that Kevin identified as having the most ground-ball heavy pitch shape in the Rays organization. When he's thrown it (which, I repeat, hasn't been often), the results have been very good. The 43% whiff rate and the 62% groundball rate, are both well above average for changeups.

If it's a pitch he can learn to be comfortable throwing, then it's an obvious candidate for an easy adjustment. Throw the pitch with the best results more, until hitters tell you that you're throwing it too much.

Promoting Ronald Belisario isn't necessarily something for Rays fans to get excited about. If he were a sure-thing lockdown reliever, he'd have signed a major league contract. But if you believe in the DIPS theory of pitching, he's someone to take a second look at, and if you believe that groundballs matter, Belisario is about as good as it gets. He's an interesting arm, and now he'll have a window of opportunity to prove himself again at the major league level. That's as good a reason to watch tonight's bullpen game as any.