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Colorado Rockies prospects: No. 15, Joe Rock

The lefty is the first player to appear on all PuRPs ballots

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15. Joe Rock (369 points, 23 ballots)

Our first PuRP to appear on every ballot this time around is Rock, the 23-year-old 6’6” lefty starter. Rock was was the 68th-overall pick of the 2021 draft and signed for a slot bonus of $953,100, and has made steady progress up the minor league ladder the last two years. He was one of the few PuRP pitching prospects with a clean bill of health in 2022, throwing 115 2⁄3 innings between High-A and Double-A in 2022. In 2023, Rock was assigned to Hartford again and was still 2.4 years younger than league average.

In a full campaign with Hartford, Rock’s run of health ended with an injury that put him on the shelf for a month from mid-April to late-May. Nonetheless, Rock bounced back and threw 90 innings across 19 starts for Hartford (none of them crossed the 100-pitch plateau). He posted a 4.50 ERA with a much lower 3.44 xFIP in those innings, accompanied by a 1.40 WHIP, 10.8 K/9 rate, and 3.2 BB/9 rate. Rock went 1-10 on those starts, but that’s not too surprising given he only once pitched into the seventh inning.

Rock’s Double-A rates were marred by a 6.18 ERA in his nine home starts (3.20 on the road) and the fact that lefties actually hit better against him (.289 BA) than right-handed batters (.259). He also got a late-season start with Triple-A Albuquerque, though it only lasted 2 23 innings with three runs on three hits, two walks, and four strikeouts.

Here’s some video of Rock from July 2023:

FanGraphs ranks Rock 15th in the system as a 40 FV prospect:

Rock has an ideal pitcher’s build and an incredibly loose and fluid delivery for a guy his size. … His frame, small school/cold weather pedigree and the missed year of reps were all late-bloomer traits that indicated his already solid stuff could become better with pro development.

Rock’s fastball touches 96 mph, sits 91-94, and has tailing action that’s aided by his natural deception. It takes hitters a few looks from the batter’s box to really seem comfortable in there, especially the lefties. There have been flashes of an above-average slider and changeup, though Rock’s finishing pitch has been his slider to this point. His slider command is much more advanced than that of his changeup, but the changeup’s action is better when he releases it correctly. It’s imperative for Rock’s changeup to develop, as it will help keep righty hitters off his fastball, which they get a nice long look at due to his arm slot. He has a leg up in this regard because of his mechanical fluidity and tailing fastball shape, which mimics that of his change. Even with a fully developed changeup, Rock’s fastball may end up playing best in shorter bursts rather than two and three times through a lineup, but at the moment, he has a shot to pitch toward the back of a rotation.

Rock was ranked 16th in the system by MLB.com in their 2023 list as a 45 FV prospect:

With three pitches coming from his long and lanky 6-foot-6 frame, Rock provides an uncomfortable at-bat. He’s generally in the low 90s with his fastball, though he can reach back for more on occasion, and it plays up because of extension, deception and a slightly funky/lower slot. He can throw it to both sides of the plate, and it comes in with a bit more ride to it than hitters expect. Both his slider and changeup play well off the heater, the breaking ball being a bit of a hybrid between a power curve and slider and the changeup coming in with a lot of sink to offer a really good weapon against right-handed hitters.

Because of the unorthodox nature of his delivery, not to mention his long limbs, Rock can struggle a bit with his command, but he’s around the zone more often than not, and he has an idea of how to mix all his pitchers to keep hitters off-balance.

Keith Law of the Athletic ranked Rock 17th in the system in February 2023:

Rock shows three pitches with a low-90s fastball, average slider, and above-average changeup, but works with 40 command and doesn’t show great feel for using his stuff. He was a disaster from the stretch last year as well. He has the stuff to start but the lack of command and feel probably points to relief.

Rock was listed as a 40 FV prospect (outside the top 14) by ESPN.com in February 2023:

Rock is a 6-6 lefty who popped up at mid-major Ohio in the 2021 draft spring and eventually went 68th overall. He has a solid-average three-pitch mix and fringy command, though some scouts worry his arm action portends command and injury issues down the road.

Baseball Prospectus listed Rock 20th in the system in their November 2022 write-up:

A long, lean, fastball/slider lefty with a bit of deception, Rock leans heavily on his mid-80s breaking ball, which shows sharp two-plane break and has above-average projection. His fastball sits low-90s, but there might be more in the tank either in short bursts or given more physical development. The fastball is merely around to set up the slider, as Rock doesn’t have much command of or carry on the pitch. He will probably stay stretched out for another season as a starter in Hartford, but his eventual home will be working the middle innings out of the bullpen.

Rock boasts a projectable starter’s frame with a deceptive delivery. He’s shown improved velocity and feel for his change as a professional and has already made an appearance at Triple-A. I think, with his Rule 5 eligibility coming up after this season, Rock will be given a longer look at Triple-A and could be a fill-in starter option for the Rockies.

I’m a bit behind where the electorate is on Rock as a pitching prospect, ranking him 19th on my ballot as a 40 FV prospect with the pedigree and stuff weighed against the reliever risk and a lower ceiling. To ascend to a higher FV tier, Rock’s command and another secondary pitch will need to emerge to get high minors and MLB hitters out with a starter’s workload.