Roberto Osuna ascends to closer role using the rising fastball

Photo: (John Lott/National Post)

Photo: (John Lott/National Post)

By: Nick Ashbourne

Despite giving up a walk-off home run in Wednesday night's game Toronto Blue Jays closer Roberto Osuna remains one of the hardest pitchers in baseball to square up.

After spending the season as the bullpen's most dangerous weapon he has ascended to the closer role and at 20 years of age he doesn't look out of place. The hurler from Mexico has allowed two home runs all season, limiting opposing hitters to a .189 batting average and ranking 11th among relievers league-wide with 1.1 Wins Above Replacement.

In short he's excelled all year even though he's only recently earned the top job in the Blue Jays bullpen. He's seemed unflappable, showing impressive composure for such a young ballplayer and never seeming out of his depth. Arguably that's the most impressive thing about his performance, but there's also more tangible things that have made him special.

The most obvious attribute of Osuna as a pitcher is how hard he throws. The right-hander averages 96.47 mph on his fastball, so it seems likely that he should be a force out of the bullpen. Unfortunately it's not that easy.

As the Blue Jays saw with Miguel Castro, throwing hard is not enough to guarantee success. There are 34 pitchers in the major leagues today that have a higher fastball velocity than Osuna, but few of them have matched his dominance. Being able to light up radar guns is undoubtedly a positive, but it's not everything.

The young closer does have a solid changeup and a slider that shows promise, but he throws his fastball more than two thirds of the time and he's using it more and more each month.

Such heavy fastball usage could be seen as a concern. If opposing hitters know Osuna's four-seamer is coming 80% of the time you'd think they'd be able to hit it. But so far they just can't. Osuna has allowed a measly .198 average against on fastballs, and more interestingly he's gotten 34 of his 43 strikeouts with the pitch.

It's tempting to conclude that hitters simply can't catch up to Osuna's fastball, but really there's something else at play making it miss bats: its rising action.

To be clear, there is no such thing as a rising fastball. It's physically impossible because of gravity. However, if you ask hitters about rising fastballs very few of them will tell you they are a myth.

The phenomenon has been examined by physics experts, baseball experts, and even the television show Mythbusters

What it boils down to is an optical illusion. It is possible to throw a ball with spin that makes it drop less than expected, giving it the appearance of a rising action.

According to Baseball Prospectus, Osuna's fastball drops 11.07  inches fewer than a ball without backspin would. As a result, the ball finishes higher than hitters expect and they swing over the pitch. Texas Rangers first baseman Mitch Moreland was one of the most recent victims of this unexpected movement, striking out to earn Osuna his second career save.

Other victims have included Houston Astros slugger Evan Gattis, and Tampa Bay Rays outfielder Kevin Kiermaier.

Because of this movement Osuna has been able to use his fastball as his primary strikeout pitch, a nice luxury to have for a young pitcher still developing his secondary offerings.

Osuna is only 39 innings into his major league career and it remains to be seen if hitters will figure out his rising fastball. However, if you were going to build a pitcher from scratch a fastball with elite velocity and deceptive movement would be a pretty good place to start.

How the rest of the package develops for Osuna will determine whether he ends up as a starter or a reliever for the Blue Jays down the road, but for now the team finally has a guy who looks like he could be a reliable closer.