If Gonzalez is my favorite unranked position player prospect, then Sean Sullivan is my favorite unranked pitching prospect. Promoting Sullivan to Altoona may have looked like an unwise move to start the season. The Pirates' 8th-round pick in 2021 had a 4.68 ERA, 5.47 FIP, and 1.36 WHIP at Greensboro in 2022. But he produced an above-average strikeout rate (25.8%) and walk rate (8.3%) and was hampered by a 1.92 HR/9. But that did come with an unsustainable 26.7% home run to fly ball ratio.
Now in his age-22 season, Sullivan has been nothing but dominant through his first three outings for the Curve. He's only pitched 11.2 innings, but he's yet to allow an earned run. His strikeout rate comes in at 25.5%, and (more promisingly) he has yet to give up a home run. This is a tad surprising given that his fly ball rate is currently 52.3%, compared to just 29.9% last season. Because of that, his xFIP (expected FIP) comes in at 4.01.
While 4.01 isn't a major uptick from 3.88, his major increase in fly balls could be caused by a small sample size. His ground ball rate, for comparison, is 40%, just a 1.3% decrease from 2022. The only statistic of his that got worse was his walk rate, which went from 8.3% to 10.6%. But again, let's give him a little more time to see if he can improve his control.
Sullivan is certainly flying under the radar when you talk about the Pirates' pitching prospects. He's on track to eventually making it to Triple-A Indy later this year, and if he keeps performing anything like he has for the first month of the season, you might even see him in the big leagues. That may depend on other prospects, but still a promising development nonetheless.