Why Has Roberto Osuna’s Fastball Suddenly Disappeared?

Earlier this year, Roberto Osuna was nearly unhittable. Although he had a rough go in April, Osuna settled down shortly thereafter and made 33 appearances in which he gave up three earned runs total, all the while, striking out 39% of the batters he faced.

From late April until mid-July, Osuna had every pitch in his repertoire working perfectly. His four-seam fastball set up his slider, and he mixed in one of his newer pitches – his cutter – with great effectiveness.

Even though there was a slight dip in the velocity of his fastball, it didn’t seem like cause for concern.

After all, Osuna was using his secondary pitches with such effectiveness that it didn’t raise a lot of eyebrows at the time. But after three rough appearances in his last five games, the focus has shifted once again to Osuna’s fastball and his decision to use it less and less.

Sunday’s meltdown against the Houston Astros was the latest instance of Osuna relying on his secondary pitches (his slider and cutter) rather than his bread and butter: his four-seam fastball.

During his 21-pitch appearance on Sunday, Osuna leaned heavily on his slider (14 of 21 pitches) and opted to use his four-seamer only three times.

The Astros put all three of those four-seam fastballs from Osuna in play for hits. Coincidentally, the Astros have been a tremendous fastball hitting team this year, punishing opponents to a .377 wOBA this season, which is tied for the third best in baseball.

Looking at Osuna’s pitch type breakdown comparison between this year and last, it’s apparent he’s pulled back significantly on his four-seam fastball usage year-over-year and upped the usage on his slider, cutter and two-seamer.
 

Roberto Osuna Pitch Types (2016-2017)

Throwing 30.3% less fastballs from one season to the next would sound a few alarms for any pitcher, let alone for a relief pitcher whose pitch selections are often solely based off the fastball.

If you thought Osuna was going to his secondary stuff more frequently this season, you’d be right, but I didn’t expect the differences to be that drastic.

Another slight difference is the dip in velocity from year-to-year. Last year, Osuna’s fastball velocity averaged around 96.4 MPH. This year, it’s down about 95 MPH. Since the All-Star break, Osuna’s four-seam velocity is down to 94.07 MPH.
 

Roberto Osuna 4-Seam Velocity (2015-2017)

That means the Blue Jays’ closer either isn’t confident in his fastball (whether it’s location or the velocity of the pitch) or he’s leading heavily on his secondary pitches to get outs. It may in fact be a little bit of both, with a slight edge towards the former of the two.

It may only be a slight dip in velocity, but hitters have caught on Osuna isn’t missing as many bats with his four-seamer in 2017 as he did in 2016. Last year, Osuna got opponents to whiff on 7.94% of the four-seamers he threw. This year, that’s been chopped in half, down to 3.82%.

It seems like Osuna is cognizant of the fact that his velocity is down slightly compared to last year, which is likely why he’s increased the use of his secondary pitches not only to miss bats, but to simply get outs in general.

Not to mention, Osuna is only 22 years old. This isn’t a reliever in his late twenties or early thirties where a dip in velocity may be an indication of a bigger problem. Osuna is far too young in his career to start losing miles per hour off his fastball already.

This may ultimately just be a blip on the radar for Osuna: prior to this rough patch, he performed at Craig Kimbrel or Kenley Jansen-esque elite level for close to three months of the season.

However, if you’re a reliever, especially a high-leverage reliever, if you don’t have confidence in your fastball – the building block for all pitchers – then what confidence do you have?

Hat tip to Keegan Matheson of MLB.com for helping me out with navigating Osuna’s Baseball Savant numbers. Follow him (if you aren’t already, but come on, you probably are): @KeeganMatheson.