Breaking down Bobby Miller’s start to his rookie season

Big things were expected of Dodgers rookie pitcher Bobby Miller upon his MLB call up on on May 23rd. He’s shown some flashes, highlighted by allowing only two runs in 23 innings over his first four starts. But he’s also displayed some growing pains, allowing four or more runs five times in his 16 starts.

Those struggles are expected for a rookie pitcher as few walk into the league and dominate. However, it is enough of a sample size to judge his pitch arsenal and predict some tweaks we might see made to it down the road.

Pitch #1: Four-seam fastball, 2023 usage rate - 26.5 percent

2023 stats - .290 xBA, .484 xSLG, .358 xwOBA

Average velo - 99.1 MPH - Spin rate - 2,331 RPM - vertical movement - 11.3 inches - horizontal movement - 8.6 inches

Despite this being his most-used pitch, Miller’s four-seamer has been hit hard throughout the season. Even with his struggles his usage rate with it has spiked significantly over the past two months. In June it was just 12.1 percent, in July it spiked to 33.6 percent and in August it reached 39.5 percent. His expected metrics have been up and down going with the xwOBA going from .383 to June to .312 but then jumped to .368 in August.

Miller has been a more aggressive pitcher with his four-seamer, throwing it in the strike zone at rates of 59.8 percent and 56.5 percent in July and August respectively compared to 38.2 percent in June. Over time, I would like to see Miller throw this pitch a bit less because of how good the rest of his repertoire is.

Pitch #2: Sinker, 2023 usage rate - 21.3 percent

2023 stats - .271 xBA, .422 xSLG, .354 xwOBA

Average velo - 98.8 MPH - Spin rate - 2,295 RPM - vertical movement - 14.1 inches - horizontal movement - 13.8 inches

This pitch has excelled at working batters onto the ground. His groundball rate on it is 56.9 percent, the second-highest amongst his pitches. Notably, this is his fourth-lowest used pitch against left handed batters as he throws it just 15.7 percent of the time to them. In his 24 at-bats against lefties though they have just an xBA of .216 and xSLG of .412. Both of those numbers are significantly better than the xBA of .280 and xSLG of .468 his four-seamer have posted against lefties. Over time I would like to see the usage rate on his sinker rise somewhat significantly against left handed hitters.

Pitch #3: Slider, 2023 usage rate - 19.7 percent

2023 stats - .236 xBA, .346 xSLG, .277 xwOBA

Average velo - 90.2 MPH - Spin rate - 2,511 RPM - vertical movement - 32.1 inches - horizontal movement - 4.6 inches

Miller’s slider is largely thrown against right-handed hitters with a usage rate of 31.7 percent, his most-used pitch against them. Righties have really struggled to barrel up this pitch as the barrel rate (optimal launch angle and exit velocity) of just 2.5 percent which is far and away the longest amongst his five most-used pitches. I love how this profiles against right-handed batters and would not be opposed to his usage rate with it rising more against them.

Pitch #4: Curveball, 2023 usage rate - 17.6 percent

2023 stats - .175 xBA, .297 xSLG, .222 xwOBA

Average velo - 80.8 MPH - Spin rate - 2,824 RPM - vertical movement - 55.8 inches - horizontal movement - 9.8 inches

For as good as Miller’s curveball is, it does not lead the pack in any main statistic. Amongst his five most used pitches it is second in whiff rate, xwOBA, chase whiff rate and third in chase rate. Overall though it is a fantastic pitch, but it is just not at the level of his changeup which we will get to shortly. Miller’s spin rate of 2,824 RPM ranks 11th amongst pitchers with at least 250 plate appearances against.

I think this is a pitch that Miller should throw more often in part because of how well it plays off of his elevated four-seamer. If Miller gets more aggressive with this pitch and throws it for strikes at the bottom of the zone it could not only improve this pitch but also his four-seamer.

Pitch #5: Changeup, 2023 usage rate - 14.0 percent

2023 stats - .161 xBA, .191 xSLG, .191 xwOBA

Average velo - 88.9 MPH - Spin rate - 2,277 RPM - vertical movement - 25.8 inches - horizontal movement - 17.4 inches

The changeup is the best pitch in Miller’s arsenal. It has his best expected metrics but it also has his highest groundball and whiff rate. In addition to that, the horizontal movement on it ranks 11th amongst pitchers who have thrown a changeup 100 or more times this season. The xSLG for his changeup ranks seventh out of 211 pitchers to have 25 or more plate appearances against that pitch and his xwOBA ranks 10th when using the same criteria. If Miller can get his changeup usage closer to the low 20’s and drop his sinker to a similar number I think it would make both pitches even better because of how they would play off of each other.