Concern for George Kirby? A Vintage Lance McCullers Jr. Performance

George Kirby, Lance McCullers Jr, Drew Rasmussen

• Mariners George Kirby has had a pair of rough outings after starting the season on the IL. His arm angle is down from 37° last year to 33° in these two starts. 4° degrees feels right on the border of relevance, standard deviation in a given season for a pitcher is ~2-3°. His four-seam shape is now slightly more two-plane. He’s traded 1” of vertical break for 1” of added arm-side movement. The pitch now averages 14.5” vertical break and 11” arm-side movement at 96 mph. FanGraphs Stuff+ thinks something is wrong, pulling his four-seamer down from 103 to 89 and his overall Stuff+ from 104 to 99. He got clipped by lefties on his four-seamer twice Wednesday, one away and one inside. Both weren’t misses in my eyes. Despite the change in shape, small-sample swing-miss on the pitch is up compared to last season. He’s executing it well at the top of the zone. What is taking the hit in terms of performance drop are his non-fastballs, but the sample remains too small to overreact from a performance standpoint. 🔱

  • If we believe in any 2-start sample signal, Kirby is throwing a touch more curveball and slider to left-handed hitters. His slider to righties isn’t crushing hitters like it did in the second half last season. Both are things to watch moving forward. I’d also keep an eye on this modified fastball shape and its performance against lefties. His struggles are mostly a byproduct of being injured to start the season, I would guess. Not enough here for me to panic.

• Astros Lance McCullers Jr with a vintage performance Wednesday, going 6 IP, 5 H, 3 ER, 12 K against the Athletics. This is back-to-back games with 40%+ sweeper usage. In his prior 3 outings, he used the pitch just 25%. The majority of this change is a flip in lefty approach. He’s cut his changeup usage in half to 19% after posting mediocre whiff numbers on it in two-strike spots. His lefty approach has been heavy curveball-sweeper in his last two starts, and it’s working. His swinging-strike rate has doubled to 22% in these two outings. 💫

  • The overall concern here is the low strike and zone rates, strongly connected to the use of his quality breaking balls in place of more zone-happy fastballs. It’s the issue these arms run into by accepting that their breaking balls are their only path toward posting a better-than-league-average ERA. There’s a large range of projections on McCullers Jr given his absence from the league for consecutive seasons. The range hangs between 3.75 and 4.40. I’ll lean toward the high side of that window given prior health and the volatility of a chase-centric breaking-ball approach.

Lance McCullers Jr Grips (2025)

• Rays Drew Rasmussen posted a 1.98 ERA with a 4.63 FIP in 5 May starts. There’s likely some regression coming here, but I wonder if he can push it off by pulling back on his four-seamer to left-handed hitters. He threw the pitch 33% in April to lefties and pushed it up to 54% in May, taking the majority of that usage from his slider. This approach permeated most count-states, but was more noticeable when Rasmussen was behind in the count (40% to 62%). His swinging-strike rate versus lefties in May decreased with this strategy, but his contact quality remained fantastic. 🤔

  • I’m a bit perplexed why the move away from his slider to lefties happened, given the pitch performed well in April. Perhaps the two-strike performance of his four-seamer over his slider (26% whiff vs 15% whiff, respectively) played a part in believing the fastball would work outside of that count more. There’s room for more slider and the hard death-ball shape curve he’s throwing, especially when he’s ahead. Let’s see if he sticks with the four-seam-heavy approach to lefties in June.