The Pirates continued their slow, methodical approach to Keller's development in 2018. Keller encountered little resistance at any point during his time with Double-A Altoona -- he allowed more than three runs just twice in 14 starts -- but nonetheless the team waited until the final day of June to bump him up to the next level. While the results took a turn for the worse after the leap to Triple-A, the peripherals were fine (24.2 K%, 0.52 HR/9). Keller's walk rates haven't been especially good at the higher levels, but he commands the fastball well. Fastball command is something a lot of young arms struggle with upon arrival to the big leagues, but that shouldn't be too much of a concern with Keller. He can keep the ball on the ground and the strikeout totals should be useful, if unexciting. Considering his path to this point, it seems likely that Keller will spend much of the first half back at Triple-A before finally cracking the big-league rotation.

Keller commands one of the best fastballs in the minors -- a mid-90s weapon with late life that can miss bats in and out of the zone. The pitch is so good that it’s all he needs to get through a minor-league lineup once and sometimes even twice. He also features a potentially plus curveball that works as an out pitch, but his changeup lags well behind as a fringe offering. His top two pitches and excellent command will carry him to the majors, but he needs to improve his changeup to reach his ceiling as a top-of-the-rotation horse. A back strain caused him to throw fewer innings in 2017 than in 2016, but he went to the Arizona Fall League to build up his innings in advance of what is likely to be his final season in the minors. He had a chance to generate a lot of hype in the AFL, a la Brent Honeywell last season, but evaluators weren’t particularly impressed by his showing, even though the stats were impressive.

The Pirates 2016 Minor League Pitcher of the Year, Keller compiled a 9-5 mark with a 2.35 ERA and 1.09 WHIP in 130.1 innings split between Low-A and High-A. Perhaps even more impressively, he posted a 138:19 K:BB. The 20-year-old didn't allow a single run in six of his last seven starts, including two postseason outings. He offers a mid-90s fastball, above-average curveball and a solid changeup that serves as his third-best pitch. He struggled with his control as a rookie in 2015 (16 walks in 19.2 innings) but control wasn't an issue last year. Additionally, he managed to stay healthy in 2016 after forearm issues sidelined him for most of his second professional season. Keller will likely start 2017 at High-A Bradenton with a potential midseason move to Double-A. The 2014 second-round pick is as exciting as organization mate Tyler Glasnow, but for different reasons. Glasnow's top selling point is his ceiling while Keller's is his mid-rotation floor.

A second-round pick in 2014, Keller appeared in only 19.2 innings for Bristol last year because of forearm tightness. The results weren’t promising (5.49 ERA, 16 walks) but it’s possible the 20-year-old righty might be suffering from a more severe injury. He showed promise in 2014, registering a 1.98 ERA in 27.1 innings, but the fact that he saw so little action last summer gives cause for concern. Keller offers swing-and-miss stuff, but he needs to stay on the diamond throughout 2016 to maintain his prospect status.

A second-round pick in the 2014 draft, Keller got his first taste of professional action in the Gulf Coast League. The 18-year-old right-hander registered a 1.98 ERA and 1.17 WHIP in 27.1 innings with a 29:13 K:BB ratio. He reaches the mid-90s with his fastball, but struggles with control issues. Keller, who received a $1 million signing bonus, is expected to pitch in rookie ball for Morgantown in 2015.