Let’s look at our newest relief pitcher.
Who is the tallest relief pitcher for the Diamondbacks? Gavin Hollowell was claimed off waivers from the Rockies and immediately optioned to the AAA Reno Aces. At 6 feet, 7 inches, he is the tallest pitcher with the Aces. When he gets called up to the Diamondbacks, he and Miguel Castro will be tied for the tallest pitcher.
What is his fastball velocity? Assuming his velocity is unchanged from 2023, if he joined the bullpen on 22 June, his 4-seam fastball’s 93.4 MPH velocity would be the fifth highest in the bullpen (behind Martinez, Vieira, Ginkel, and Jarvis). The same is true of his sinker’s 94.1 MPH velocity. His velocity plays well because his long extension towards the plate (87th percentile). Worth noting is that his fastball’s spin is at the 96th percentile.
How old is he? He is 26 years old. If he joined the bullpen on 22 June, he would be the third youngest behind Justin Martinez (age 22) and Bryce Jarvis (almost 2 months younger than Hollowell). With 2 options left, he could shuttle between Reno and Phoenix this season and next season.
What is his split for left-handed and right-handed batters? Last season, he pitched much better against right-handed batters. As a point of reference, the table shows this season’s average for Diamondbacks’ relievers. The following table shows the dramatic difference:
2023 & 2024 thru 20 June. Data from Baseball Savant.
The bottom of the table shows whether the homers were against fastballs or sliders. Very notable is that left-handed batters hit 4 home runs against fastballs in only 54 PAs. Perhaps that is a fixable weakness.
Why will he will pitch better for the Diamondbacks than the Rockies? Two reasons. First, Chase is at a lower elevation and his fastball spin (96th percentile) will result in more movement making his fastballs harder to hit. Second, better defense (Outs Above Average). This season the Diamondbacks’ 24 OAA ranks best in the Majors (Baseball Savant, 21 June) which is much better than the Rockies, who last season had a negative 1 OAA (ranking 16th in the Majors).
How well did he pitch in higher leverage games? In September of last season, he pitched in 7 higher-than-average leverage games (aLI >1). Got-the-Job-Done (GTJD) is my stat that looks at what percentage of his appearances did he allow zero earned runs and zero inherited runners to score. His 71.4% GTJD in those higher leverage games was great. The following table compares higher leverage GTJD (his September to Diamondbacks relievers this season through 21 June.)
2023 and 2024 thru 21 June. Data from Baseball Reference.
How does his 2023 performance compare with the 2024 average of Diamondbacks relief pitchers? Against right-handed batters, he is better than average in nearly everything. Against left-handed batters, he gets more whiffs and gives up less hard hits, but his OBP and SLG are worse than average. Perhaps this is a situation where having a better defense supporting him could make a difference.
What does he do well and not so well? Although I’m confident he has improved in the last year, let’s take a brief look at the past. Over a year ago (December 2022), Mario DeGenz of SB Nation wrote about Hollowell in order to make a game plan.
A super-short preview of his positives (see his article for the full version) follows:
Plus sweeping slider. It “routinely pushes 15 inches of sweep…because of Gavin’s sidearm slot, it creates very extreme horizontal angles on right-handers.”
Elite extension. He has “truly elite extension..his perceived fastball velo in the 94-96 MPH range…”
Different release point. “…putting his release point at about the same height as Jake Bird’s…can create flatter vertical approach angles (VAA) than usual…”
Fastball utility. “When he threw a few cutters in his last outing of the season at LA, Hollowell completed the trinity of fastballs: a sinker, a cutter, and a four-seamer. And while none of them stand out in theory as dominant offerings, the fact that he has all three gives him terrific utility to attack all kinds of hitters.”
Good control. We’ll see how this evolves moving forward, but I have no concerns about wildness costing him dearly
A super-short preview of his negatives (see his article for the full version) follows:
His fastballs are mainly situational pitches. “…none of Gavin’s fastballs are truly dominant pitches in a vacuum, and their success is likely to depend on being used in the right matchups.”
Unclear changeup feel. “Hollowell threw just three changeups in his brief big league cameo,…”
Summary.
Gavin Hollowell is very tall and relatively young.
His fastball velocity is about average, but his elite extension makes it appear faster.
In September, he pitched well in high leverage games.
He could pitch better for the Diamondbacks for two reasons:
- His high-spin fastballs at the lower elevation will make his fastballs harder to hit.
- The Diamondbacks have better defense supporting him.
Against right-handed batters he pitches better than the average of Diamondbacks relievers. Comparing his performance against left-handed batters is more mixed: more whiffs and less hard hits, but worse OBP and SLG. Left-handed batters hit homers more frequently.
Another SB Nation article talked about what he does well. I’m confident that he improved in the following year and a half.