McWilliams was recently sent to Tampa Bay as a PTBNL, part of the three-team deal that sent Steven Souza Jr. from the Rays to the Diamondbacks. This marks McWilliams’ third team since being drafted out of a Tennessee high school by the Phillies in 2014, as he initially was dealt from Philadelphia to Arizona in the 2015 trade that brought Jeremy Hellickson to the Phillies.
I saw his final start as a D-Backs prospect, suiting up for High A Visalia in the Ca League. McWilliams’ fastball is very effective when he’s able to his his spots, working at 94-to-96 mph with above-average tailing life. He will wrinkle in a true two-seam fastball at 92-to-93 mph with more arm-side movement, especially when there are runners on and he’s working for a ground ball. Despite plus arm strength and two looks at his fastball, the overall value of his heater projects closer to average: fringy in-zone command plays it under its velocity, allowing hitters better passes than you’d expect.
McWilliams works with a four-pitch mix, showing both a slider (86-88) and true curveball (82-85) along with a changeup (86-88). His slider is the best secondary pitch, showing sharp bite that gets hitters to chase out of the zone when he’s ahead in the count. He has a hard time landing it for early-count strikes, and it’s tough to project the slider as a true 60-grade offering given that he can only use it with two strikes. The 6’7” righty struggles to repeat his delivery and battles periods of wildness, and while the curveball and changeup show their flashes, the inconsistent execution of both means that McWilliams sometimes falls into being just a two-pitch starter.
With two average to solid-average pitches in the FB/SL combo, I see McWilliams fitting a middle-relief profile. He’s currently a starter, but focusing on a two-pitch mix and command seems to be the route where he would have most impact. Given his size and ability to at least flash a full starter’s four-pitch mix, he could probably make emergency starts or pitch numerous innings during mop-up situations. He fits the bill of a Role 45 system: a lower-ceiling arm, though one who could potentially contribute in a variety of roles.