SF Giants observations: Mahle working on slider, Haase hits grand slam

MESA, Arizona — With a revamped slider in his bag, Tyler Mahle made his first appearance in a Giants uniform on Saturday afternoon at Hohokam Stadium, tossing a scoreless inning with two strikeouts.

Mahle, who signed a one-year, $10 million deal to join San Francisco this offseason, has thrown a slider of some kind for most of his career. But the current version of the pitch, which he threw six times on Saturday, had more movement compared to last season.

Against the Athletics, Mahle generated eight inches of glove-side movement. In 2025, by contrast, Mahle only generated 3.2 inches of horizontal movement with his slider. So far, the returns have been encouraging. Three of the six sliders that he threw generated a swing-and-miss (one striking out All-Star Jacob Wilson) while another landed for a called strike.

“Last year, I had a cutter. It wasn’t a very good pitch but it had its purpose, which is a big part of it, too,” Mahle said. “But to get (the slider) to expand a little bit more glove-side is something I worked hard on.”

Mahle tried throwing a sweeper in 2023 before undergoing Tommy John surgery, and while the pitch generated 8.9 inches of horizontal movement, the right-hander believes the pitch could’ve led to elbow discomfort because he threw the pitch differently than his normal arm path. The tweaked slider, by contrast, he throws with a “hard curveball feel.”

“I’d faced him a couple times in the past,” said catcher Eric Haase. “He had a noticeable step in his slider, if you want to put it that way. Where he was throwing the pitches today, the command was fantastic, even his misses. Everything you’d hope to see from him. If we can make that translate into 150 (innings) this year, I think he’s going to be in a great spot.”

The 31-year-old Mahle missed his first go-around in the rotation of Cactus League play because he felt under the weather. Despite missing the start, Mahle shouldn’t be too far behind his fellow starters.

“I think there’s something to a guy like Mahle starting the game and having a calming influence,” said manager Tony Vitello. “It wasn’t a perfect inning, but just the approach.”

McDonald continues to impress with perfect outing

Right-hander Trevor McDonald made his latest case for the Opening Day roster, throwing two perfect innings with three strikeouts.

McDonald’s average sinker velocity against the Athletics (93.4 mph) wasn’t as hot as his first outing of Cactus League play (95.2 mph), but he landed his sinker and slider for strikes and generated four whiffs.

“When these come out of the pen and they’re just filling up the zone, they’re very nasty, hard to it,” Haase said.

While Baseball Savant lists McDonald as throwing a curveball, McDonald confirmed that he’s actually throwing a slider.

Haase makes impression with grand slam

Following Victor Bericoto’s no-doubt grand slam on Friday, Haase hit a grand slam of his own against the Athletics’ Eduarniel Núñez, one of two hits he had on the day.

“Just trying to get something in the air, and for it to carry out of there is always a plus,” Haase said. “The approach was better and the timing was a lot better today.”

Daniel Susac appears to be the favorite to make the Opening Day roster as Patrick Bailey’s backup catcher due to his Rule 5 Draft status, but Haase has a compelling case in his own right. The 33-year-old Haase is the most experienced catcher in camp, having played 383 games over eight seasons in the majors.

“It doens’t matter how many years you’ve played in the league. You get to where you don’t get immediate results or you don’t get a few strung together, you start pressing,” Vitello said. “Even in (batting practice) on the field, Haase was pressing on the field a little bit. But I think his determination kind of suppressed that. He just came out here and played ball.”

Pair of top prospects turn two

Shortstop Josuar Gonzalez and second baseman Gavin Kilen, Baseball America’s respective No. 2 and No. 9 prospects, won’t get a ton of playing time during Cactus League play, but the duo combined turned a 6-4-3 double play in the bottom of the ninth inning.

“It was great to see,” Vitello said. “I know that they’ve been working really hard, so it’s good for them to get rewarded and just get a little taste of the action.”

Gonzalez, 18, ended up stranded on the on-deck circle when Jesus Rodriguez made the final out in the top of the ninth, but Vitello said the Giants will try to get the shortstop an at-bat at some point. Kilen, who played under Vitello at Tennessee, grounded out in the top of the eighth inning.