In this year’s postseason, relievers have received attention based on when (or if) they have entered the game. For the Toronto Blue Jays and closer Roberto Osuna, there were questions a week ago whether Osuna would be able to pitch at all in the postseason after being removed from the Wild Card victory over the Baltimore Orioles with a shoulder issue. Osuna pitched to four batters in that game, retiring them all and striking out two, but his availability for the recently completed Division Series against the Texas Rangers was in some doubt. Osuna has laid those doubts, as well as those that accompanied a less-than-stellar end-of-season run, to rest.

If you were to hazard a guess at which Blue Jays player was most important in this year’s playoffs — at least in terms of increasing the probability of winning games — you probably would not guess Roberto Osuna. You would also be right not to guess Osuna, as Josh Donaldson’s nine hits and a walk in 19 postseason plate appearances led to a team-leading .635 WPA over the Jays’ four postseason games. Osuna, however, is second on the team WPA leaderboard, despite pitching in only three of the four games and recording just five total innings.

Osuna, despite his shoulder issue, has now appeared in three of the four Blue Jays playoffs games (having not been needed in the Game 1 rout of the Rangers). In this year of the non-traditional closer use in the postseason, Osuna has yet to come in at the start of the ninth in a save situation. Every single appearance has been incredibly important — and has often coincided with the most important moments of each game, by leverage index.

Roberto Osuna Playoff Appearances Game Situation Runners/Outs IP First Batter LI Highest LI in Game WC Game T9 (tied) 0/0 1.1 2.32 2.32 Game 2 ALDS B8 (up 5-3) 2/1 1.2 2.73 3.30* Game 3 ALDS T9 (tied) 0/0 2.0 2.32 2.74 *The 3.30 LI occurred with Osuna on the mound in the ninth.

In the playoffs this year, Blue Jays pitchers have faced 15 batters at a point in the game when the leverage index had reached 2.0 or greater. Osuna has recorded eight of those high-leverage plate appearances — more than J.A. Happ (who had four in his start), Francisco Liriano (one), or Joe Biagini (two, one of which was a run-scoring double by Mitch Moreland in Game 2).

That Osuna has pitched well in the playoffs isn’t in doubt. In five innings, he’s faced 16 batters and struck out six, giving up only one hit, a leadoff double to Adrian Beltre in the ninth inning of Game 2 against the Rangers. Whether Osuna would be able to pitch at all was in considerable doubt over the past week — and the final few weeks of the regular season added to those concerns.

On September 21, Osuna struck out all four batters he faced in the ninth and 10th innings of a 12-inning game against the Seattle Mariners — a game that Toronto would ultimately lose. Osuna’s WAR stood at an even 2.0 at that point. He’d recorded a 3.00 FIP (69 FIP-), a 2.42 ERA (57 ERA-), and had struck out 31.3% of batters while walking just 5% of them. Over the last six games of the season, however, Osuna faced 29 batters and fanned just one. He also only gave up just one walk and four of the six outings were scoreless, perhaps masking some of Osuna’s issues. Alternatively, there might have been no issues at all. This poor run of form might have been just a random blip in a long season.

Osuna, just 21 years old, has already pitched significantly more innings in the majors (157 IP, including postseason) than he did for the Blue Jays in the minors (89.1 IP), and the possibility that Osuna was wearing down as the season progressed is a real one. Here is Osuna’s cumulative WAR on the season, which began to stagnate even before September 21:



While a few poor outings can hurt relievers given their smaller sample of innings, WAR is a product of fielding-independent numbers, not mere runs allowed — and the cause of Osuna’s decreasing WAR appears to be the product of a similar decrease in strikeouts. Here is Osuna’s 10-game rolling K/9 this season.

Osuna’s velocity held through September, continuing to sit at about 97 mph on the fastball, though a couple outings did produce figures below that average, per Brooks Baseball. What did happen in September is that Osuna’s slider stopped getting whiffs, dropping from 30% over the first five months of the season to just 11% over the final month, leading to a corresponding drop in strikeouts. Osuna did some experimenting as the season went on, speeding up and slowing down his delivery. He also greatly increased his sinker usage.

Through September 1, Osuna had thrown 27 sinkers on the season; he threw another 27 in the season’s final month alone. That heavier sinker usage has continued through the postseason, sprinkled in among his normal four-seam fastball and his usually deadly slider. Whether sinker use has had any great effect is tough to tell, but we do know that his slider is getting the production it got for most of the season and that his average fastball velocity is higher now than it was during the regular season.

While it would be irresponsible to read too much into five playoff innings, it should be comforting to see that those five playoff innings are much closer to the Osuna that we saw in the regular season. The slider is working. The velocity is there. While the sinker is an interesting dimension with unclear results, that Osuna’s results and velocity match up with the good part of Osuna’s season is a real positive. The other positive for Blue Jays fans is that the sweep just bought the team and Osuna a bit more rest. Osuna might have been taxed as the regular season drew to a close, highlighted by less-than-stellar strikeout numbers and a shoulder concern in the Wild Card game. Osuna has rebounded in the division series and, with more time, it appears safe to trust Osuna in big moments at the end of games.