Diamondbacks Top Prospects #7: LHP Blake Walston

Walston initially struggled with the homer-happy environment in Double-A Amarillo, but finished the year strong.

Name: Blake Walston

Age: 21

Position: Starting Pitcher

Acquired: 2019 MLB Draft, 1st Round (26), $2.45M signing bonus

Tools and Grades: Fastball 50, Curveball 60, Slider 60, Changeup 55, Command 50, Overall 50

Walston stands at 6'5" and is very athletic, allowing for a smooth and repeatable delivery. His fastball sits in the low 90s, but he can reach back for 97 when going for punchouts. The curveball, a mid 70s big bender, has always been his best secondary pitch in his career, however the slider made significant progress in the second half of the season. It's a very effective pitch against lefties and he's had success throwing it to the back foot of righties. The emergence of the pitch gives Walston potentially three swing-and-miss pitches (fastball, curveball, slider). He also features a changeup, which he has a good feel for but hasn't used much in his career as he's been working on his slider.

ETA: 2023

Risk: Medium

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2022 Season Overview

Walston opened up the year with High-A Hillsboro, but only made four dominant starts before getting the promotion to Double-A Amarillo for a more appropriate challenge. The extreme homer-friendly park gave Walston trouble early on, as he coughed up seven runs in his first start in Hodgetown. In his first 11 Double-A starts, Walston was 2-3 with a 7.69 ERA with a 50/22 strikeout to walk ratio in 50.1 innings. Opposing hitters had a .430 BABIP and Walston nearly walked 10% of the hitters he faced. 

After the All-Star break, Walston really came into his own. In his final 10 starts, going 5-0 with a 2.89 ERA and a 60/17 strikeout to walk ratio in 56 innings. Walston's strikeout rate improved from 21.6% to 26.4% while cutting down his walk rate from 9.5% to 7.5%. Additionally, the BABIP allowed dropped to .248 over that stretch. Neither BABIP number is sustainable over a long stretch, but it's a sign of improved stuff and command turning into better results. 

2023 Outlook

Walston will likely be pitching for Triple-A Reno by the end of May, if he doesn't open the season there. If he can repeat the similar strikeout and walk numbers as his final 10 starts in Amarillo, he will be eligible for a promotion to the big leagues in the second half of the season. Reno presents a similar challenge to Amarillo, where there are some parts of the ballpark where fly balls get caught up in the wind and carry over the fence. Some of the road parks in the Pacific Coast League are also hitter-friendly, with Las Vegas being worse than Reno due to the dry climate.

Since he will be Rule 5 eligible after the season, I expect the Diamondbacks to call up Walston before the end of September just to see how he fares against big league hitters. They followed the same process last year with Drey Jameson and Ryne Nelson, both of whom were able to handle the big leagues in their first cup of coffee. If there comes a situation where Madison Bumgarner is no longer able to pitch well enough to keep a roster spot, Walston is a candidate to be added to the rotation even earlier than September if he performs well in Reno.

MLB Projection

Walston still has some physical projection left in his frame, although there isn't much more he can add to a 6'5" 207-lb. frame. Walston has a chance to develop four above-average pitches, with both his breaking balls being plus. Being both left-handed and having a full arsenal of pitches, Walston has a very strong chance of sticking in the rotation long term. If his fastball develops into a plus pitch, he has top of the rotation upside but is likely to settle more into a #3 starter.