What a makeover Garrett Crochet has undergone over the last year.

At this time last offseason, Crochet was an injury-plagued reliever coming off Tommy John surgery and shoulder issues, with question marks about whether he'd ever again look like the dominant rookie who was so good that he debuted for the White Sox the same year he was drafted.

Now he's a 25-year-old ace-in-the-making, one who left the bullpen for the starting rotation in 2024 and immediately became an All-Star and a 200-strikeout starter. He's a pitcher worth pulling out all the stops to get -- which the Red Sox just did, trading a haul of prospects to Chicago to land Crochet in a blockbuster.

Here's how Crochet changed the arc of his career so dramatically.

1) He didn't lose velocity ¡­ he gained it

You expect to see a velo boost when a starting pitcher converts to a reliever -- not the other way around. But that's what Crochet did. He went from the bullpen to the rotation, and he started throwing harder.

Normally, that doesn't happen. The bullpen lends itself to max-effort pitching over short bursts. When a reliever becomes a starter and has to throw a full season's worth of innings, he typically loses a little bit of that juice. Look at recent converts like Michael King, who averaged close to 95 mph as a reliever in 2023 but dipped to just over 93 mph as a starter in 2024, or Jordan Hicks, who went from over 100 mph as a reliever in '23 to under 95 mph as a starter in '24.

Crochet flipped that. He added a full mph to his four-seamer from 2023, when he returned from Tommy John surgery and was still a reliever, to 2024, his first season as a starter. Crochet's fastball velocity as a starter was even higher than it was in his last healthy season as a reliever in 2021.

Crochet's avg. fastball velocity by season

• 2021 (reliever): 96.7 mph
• 2023 (reliever): 96.2 mph
• 2024 (starter): 97.2 mph

Crochet had the fastest fastball of any left-handed starting pitcher in 2024 -- he was the only lefty starter to average over 97 mph on his four-seamer. He was also one of only three lefty starters to hit 100 mph, along with Tarik Skubal and Cole Ragans.

Armed with a more powerful heater than anyone could have expected, Crochet racked up 100 strikeouts on four-seamers last season, third most of any starting pitcher. He generated a 31.4% swing-and-miss rate with his four-seamer, the highest of any starter with at least 500 swings against their fastball.

2) He expanded his arsenal

Dominant relievers often don't need a big repertoire; they just need one or two wipeout pitches. That was true of Crochet. As a reliever, he relied heavily on a two-pitch combination: fastball-sweeper.

From 2020-23, Crochet's four-seamer and sweeping slider accounted for 90% of his pitches. But it's hard to get by on two pitches when you're a starter and you have to get both righties and lefties out multiple times a game. So when Crochet moved into the White Sox starting rotation in 2024, he added new pitches.

And he didn't just add pitches, he added nasty pitches.

• New pitch No. 1: A hard cutter.

That gave Crochet a sharper weapon with which to attack right-handed hitters. His "sweeper" style of slider gets a lot of horizontal break, but that type of slow, sweeping movement tends to be a lot more effective in lefty-lefty matchups than lefty-righty matchups, because a lefty sweeper moves into the path of a right-handed hitter's barrel.

Crochet's new cutter averaged 91.6 mph. That made it the second-hardest cutter thrown by a lefty starter in 2024, just behind Carlos Rod¨®n's. It still has velocity separation from his four-seamer, over 5 mph, allowing Crochet to pound it in on righties much more effectively than he could do with his slower, 84.2 mph sweeper.

The cutter also allowed Crochet to make a change to the sweeper. He made it, well, "sweepier" than ever before. Adding the low-90s cutter as a step down from his four-seamer allowed Crochet to take some velocity off his sweeper and throw the pitch with bigger movement.

Crochet's sweeper averaged 94.3 mph as a starter in 2024, his lowest velocity on that pitch type for any season of his career. But his sweeper also averaged 39.1 inches of drop and 14.3 inches of horizontal break -- both his highest for any season of his career. With that extra movement, Crochet's sweeper generated a 42.7% swing-and-miss rate, third-highest among starters with at least 100 swings against their sweeper.

Crochet's sweeper by season

• 2020: 86.4 mph / 35.7 inches drop / 12.8 inches break
• 2021: 85.0 mph / 38.0 inches drop / 13.0 inches break
• 2023: 84.6 mph / 38.7 inches drop / 13.8 inches break
• 2024: 84.3 mph / 39.1 inches drop / 14.3 inches break

But back to the cutter. In his first season throwing it, Crochet used his cutter over 28% of the time. It instantly became his top secondary pitch against right-handed hitters. Crochet induced whiffs on a third of the swings against his cutter, and he collected 59 strikeouts on cutters -- second only to cutter maestro Corbin Burnes among starting pitchers. Not bad for Year 1 of throwing the pitch.

• New pitch No. 2: An upper-90s sinker.

That gave Crochet a different fastball look to throw at hitters, and in particular, a horizontal-breaking fastball that he can pair with his sweeper.

Crochet didn't debut his sinker until August, but once he started throwing it, it looked filthy. His sinker averaged 97.9 mph with 15.5 inches of arm-side run -- almost double the 8.1 inches of run he got on his four-seamer -- and 20.6 inches of drop. Both his horizontal and vertical movement were above-average vs. comparable sinkers.

After testing out the sinker in August (4% usage), Crochet threw it 15% of the time down the stretch in September -- including 30% of the time against lefties. He threw as many sinkers against lefties over the final month as he did four-seamers.

That usage makes sense, because Crochet's sinker breaks as much horizontally in one direction (15.5 inches) as his sweeper does in the opposite direction (14.3 inches). With his new sinker-sweeper combo, Crochet can control both sides of the strike zone against left-handed hitters.

Overall, Crochet held opposing hitters to a .154 batting average against his sinker in 2024, with just a pair of singles allowed in 13 at-bats, five strikeouts and a 32.1% swing-and-miss rate induced. But maybe most notable: All eight of the batted balls against Crochet's new sinker were ground balls. That's what you want.

Crochet's ability to add multiple new pitches -- the cutter to start the year, and the sinker on the fly late in the season -- shows his adaptability as a starter. That's a quality the Red Sox have to like.

3) He dropped his arm angle

Here's one more interesting change Crochet made as a starter last season: He lowered his arm slot.

Statcast has arm angle data going back to 2020, Crochet's rookie season. And what we can see is, he went back to the release point he had as a rookie -- the season he was the most overpowering as a reliever -- after throwing out of a more over-the-top arm slot in 2021 and 2023.

For pitcher arm angles, zero degrees is perfectly sidearm, and 90 degrees is straight over-the-top. You can see how Crochet's arm slot changed from a lower angle in his debut season -- when he was routinely wiping out hitters with 100-plus mph fastballs and nasty sweepers -- to a higher angle over his next two seasons as a reliever ¡­ and back to his original arm angle once he became a starter.

Crochet dominated with that lower arm slot as a rookie reliever. He dominated with that lower arm slot as a first-year starter. Probably not a coincidence.