Casey Mize placed on 15-day IL with right ankle sprain as Padres enter playoff push

What happened

The San Diego Padres have placed right-hander Casey Mize on the 15-day injured list with a right ankle sprain, per a team announcement reported by AJ Eustace of MLB Trade Rumors. Infielder/outfielder Gavin Sheets was reinstated from the 10-day IL to take his roster spot. The club brought right-hander Griffin Canning up from the Arizona Complex League while sending left-hander Kyle Hart down to that level. Separately, reliever Alek Jacob — designated for assignment earlier this week — cleared outright waivers and was assigned to the Complex League, moves MLB Trade Rumors describes as 40-man neutral.

Why it matters

Mize started the day before this report against the Diamondbacks, lasting four innings and allowing seven earned runs on seven hits, three of which left the yard. Per MLB Trade Rumors, Jeff Sanders of the San Diego Union-Tribune noted that Mize addressed his ankle during the postgame, indicating it was still bothering him roughly a month after the original injury.

That original incident, per the report, came on August 22nd, when Mize slipped on the dugout steps, sprained his right ankle, and was pulled after 2 2/3 innings. Across the six starts that followed, he reportedly allowed nearly eight earned runs per nine innings and gave up eight home runs — a rate of 2.70 HR/9. The combination of that performance arc and his own postgame comments appears to have prompted the club to shut him down.

Per MLB Trade Rumors, the Padres are not expected to have Mize available until Game 1 of the NL Championship Series, should they advance that far, which means his regular season is over. The report puts his final regular-season line at 131 1/3 innings, a 4.32 ERA, a 20.0% strikeout rate, and a 6.9% walk rate.

The numbers

Mize's regular-season totals, as reported by MLB Trade Rumors: 131 1/3 innings, a 4.32 ERA, a 20.0% strikeout rate, and a 6.9% walk rate. That walk rate is a genuine asset — pitchers who limit free passes at that level are exactly the kind of depth piece a club wants available in a short series, which makes the timing of this placement consequential for San Diego's postseason planning.

Where the club stands

San Diego has clinched a playoff spot — their third consecutive postseason berth, per earlier Posterior reporting — and enters play as the top Wild Card seed in the National League, per MLB Trade Rumors. A win over the Diamondbacks in the game following this report would lock in that seed and secure home-field advantage in the Wild Card Series.

The rotation picture for that three-game set is taking shape around Mize's absence. Per the report, Michael King and Nick Pivetta are expected to serve as the top two starters. Walker Buehler and Robbie Ray are reportedly competing for the third spot. Buehler carries a 4.56 ERA on the season but has posted a 3.24 ERA across his last eight starts, six of which lasted at least five innings. Ray is described as not having been sharp in nine starts since arriving from the Giants at the deadline. Per MLB Trade Rumors, Buehler is seen as likely holding the edge, which would push Ray into a bullpen role.

The upcoming schedule at Petco Park lists Buehler as the probable starter for Saturday, September 26 against the Diamondbacks, with Sunday's probable listed as TBD.

Two days before this report, the Padres had activated reliever Jason Adam from the 60-day IL, per prior Posterior reporting — a bullpen addition that carries added weight now that Mize will not be available for any potential length work in the Wild Card round.

What we don't know yet

The projected return timeline around the NLCS is contingent on San Diego advancing through the Wild Card Series, which remains unresolved. How Mize's ankle responds to rest — and whether he could be available in any capacity before that stage — has not been reported. The third rotation spot for the Wild Card Series has not been formally decided between Buehler and Ray, per the report.

What to watch

The Diamondbacks series wraps up this weekend, and tonight's result will determine whether San Diego locks in the top Wild Card seed and home-field advantage. The Buehler-versus-Ray decision for the third Wild Card start is the most immediate roster question to monitor. Should the Padres advance, Mize's ankle recovery — and whether he is available out of the bullpen in a potential NLCS — will be worth following as the postseason unfolds.