When he arrived in Arizona in 2019, right-handed pitcher Luke Weaver had a new toy. He bought a Rapsodo in the offseason and threw in front of it to figure out how to improve his throws. The problem was that he wasn't entirely sure which numbers to track on the screen. So he had a meeting with the company, got some insight into what he might be looking for, and tried to coach himself.

He focused on the curve and cutter because his drop-and-drive fastball and changeup were a proven combination. In relation to the quota, he threw more curves and cutters this year than ever before. He had a good year with a 2.94 ERA in 12 starts, but he may have been on a tricky path as he spent three of the next four seasons with an ERA over 6.00 across five teams looking for answers Slugging percentages are approaching the .700 range on his curves and cutters.

Every year brought new ideas. He threw more sliders in 2021. In 2023, he switched to a knuckle curve. The Seattle Mariners let him increase his cutter usage despite the results.

Weaver is an extreme pronator, meaning he pulls his index finger down earlier than other pitchers as his arm comes through to release the ball. He pronates earlier. Here he demonstrates what it means to be a pronator when releasing the ball:

If there are rules for throwing a good curveball – where you generally want to be supinated (with your hand on the opposite/minor side of the ball for longer) – they may not work for Weaver. Even in 2017, while working on curveballs with Adam Wainwright of the St. Louis Cardinals, Weaver said something that ended up suggesting he was having trouble mastering a good curveball.

“My body sometimes wants to release the ball too early and then it bounces up and spins,” he said at the time. Seems like something that could happen to a pronator even if he tried to release the ball forward, which is what Weaver was working on at the time.

In related news, the right-hander is throwing the curveball less than at any time since joining the New York Yankees. His fastball is better, his cutter is better… a lot is different in New York – and this time it's working, as he's gotten closer for a team that's getting closer to the World Series every day.

“It’s been a journey,” he admitted late that season. “But everything feels good now!”

The first change came almost immediately. A four-seam fastball that once had good barreling had lost its pop, and the Yankees thought they could improve Weaver's spin efficiency to get it back. A small, simple twist of the ball to bring Weaver's longer middle finger to the seam was the trigger. By using 94 percent of his fastball spin and converting it into motion, instead of the 92 percent Weaver had fallen to over the past two seasons, he immediately gave it more momentum than it had in years. That happened immediately in New York, and then a conversation with Gerrit Cole helped him really get into the process. He now has more travel on the fastball than ever before.

Since he also switched to the pen this year, he throws the ball a touch harder than ever before. Combined with his low release point due to his drop-and-drive mechanics, he has created a four-seater that features some of the best stuff in the game. He's now in the top 10 in Fastball Stuff+, which is all about the physical characteristics of a pitch, and his year-over-year improvement in four-seam Fastball Stuff+ is the best in the short history of that statistic.

A small change to the grip on the cutter also helped Weaver, although the improvement was a little more subtle. He added an inch of freedom of movement on the glove side, which is good, but nothing he didn't have on the field before. Here, however, the movement to the pin allowed him to throw the pitch two ticks harder than ever before, and the combination of that movement and that speed is the best of his career. He achieved the best results of his career on the pitch.

The biggest grip change the wiry Weaver made with the Yankees, however, wasn't to the cutter or the curve, which he had been fiddling with for ages. The Yankees even had ideas for his best pitch, the changeup. Here Weaver models the transition where he went from a two-seam alternating grip to a one-seam alternating grip:

This has resulted in the biggest drop in transfers of his career.

Weaver mentions in the clip that he gets more seam shifts with this grip, and Savant's numbers agree. They show him with the largest difference between expected and observed change in advancement in his career.

Here's the highest-drop changeup he's thrown for a swing strike this year:

It's a beauty. And for Weaver, a marker after a long, winding road through the wilderness of field design. One that involves hard work coupled with strong coaching.

“The Yankees were great,” Weaver said with a smile as he looked around the clubhouse. “Those guys were great.”

(Photo by Luke Weaver: Vincent Carchietta / Imagn Images)