Is Osuna the best reliever in baseball?

This will probably will be a somewhat controversial article as I know there are still mixed feelings on Osuna, but it warrants a discussion to me. I’m asking us to stay strictly to the baseball side of the equation for this discussion as the other side has been discussed ad nauseam.

Last year, in a controversial move, the Astros acquired Roberto Osuna. What was surprising, is that the 2018 season was a “down” season for Osuna, with some wondering if he had lost a step and should still be considered the closer, although he continued to improve as the season went by.

Now for some clarification, for most relievers in baseball, a 21 save season with a 2.37 ERA could be a career best. But there was a notable drop in strikeout rate from a career K/9 of almost 10 to 7.58, makes people wonder if something was off, or if he was just rusty and distracted.

Then the clock struck 2019. Now it’s an extremely small sample size, all of 8.1 IP so far this season, so there’s a huge grain of salt that goes into this evaluation, but he has simply been dominant enough to warrant a second look.

He’s currently converted all 19 save opportunities in the regular season since joining the Astros. His K/9 has jumped back to 9.72, and while he has always had excellent control (1.52 BB/9 for his career), he has yet to walk someone this year. His current ERA is a sparkling 1.08, his WHIP? A ridiculous 0.24 (0 walks and only 2 hits through his first 9 appearances).

On the good side, his fastball has regained a tick in velocity, throwing the hardest he has since 2016. It’s easy to forget that Osuna is only 24 years old. He’s the youngest player on our team edging out Carlos Correa by about a half a year. There’s a strong possibility that Osuna has not hit his peak yet.

So it’s easy to think, it’s a small sample size and Osuna just got lucky. I mean his BABIP is .111, which is generally indicative of pure luck. Which could very well be true, but some of the advanced stats seem to support his utter dominance.

Baseball Savant / Statcast

For those of you who don’t frequent baseball savant, they have a simple slider at the top which gives you a quick glimpse at how the player is performing. The further to the right and the darker the red, the better the player is doing (or blue for poor performance). Doing a quick look, obviously, Osuna looks dominant.

But when you look closer, he gets even better.

K%? He’s in the top 11% of the league

Exit Velocity? Top 20% of the league

Hard Hit %? Top 1% of the league

xBA? Top 1% of the league

xSLUG? Top 1% of the league

xwOBA? The best in baseball

I’m a huge fan of xwOBA. For those who aren’t familiar, xwOBA looks at the launch angle, exit velocity, sprint speed etc of every ball that was hit and based on a percentage of plays that were made at that same type of contact assigns a value to it. It removes the “luck” of a diving play or jump over the fence that saves runs, or the silly non-error that bounced between a players legs to give a more realistic view of the contribution of the player while removing the luck factor. They normalize xwOBA to look like OPS - so when you’re looking at the results,

For more info, here’s the full description and the why it’s useful: xwOBA is more indicative of a player’s skill than regular wOBA, as xwOBA removes defense from the equation. Hitters, and likewise pitchers, are able to influence exit velocity and launch angle but have no control over what happens to a batted ball once it is put into play.

Based on the contact so far, Baseball Savant would expect a .117/.117/.162 line against Osuna for a .121 xwOBA

And xwOBA say that so far, he has been the absolute best in all of baseball.