The 25-year-old Castro was ranked by MLB Pipeline as Toronto's No. 19 prospect, while Lockett, 26, has pitched in the Major Leagues for parts of the past three seasons with the Mariners, Mets and Padres. These moves bring Toronto's 40-man roster to a full 40 players, meaning that any players being added via free agency or trade will require a countermove to free up space.
While Castro is the upside play here, Lockett comes with more experience at the Triple-A and MLB levels. The right-hander has been traded twice and most recently went from the Mets to the Mariners on waivers in September. He has posted a career 7.67 ERA in the big leagues over eight starts and 12 relief appearances.
The majority of Walker’s time in the Minor Leagues has come as a starter, and he has spent parts of the past four Minor League seasons at the Triple A level. There, Walker has posted a 4.40 ERA over 47 appearances with an impressive walk rate of just 2.0 per nine innings. Spots on the 40-man roster will be valuable this offseason but, for now, Lockett can be considered as starting depth with some versatility for the Blue Jays.
Castro, on the other hand, has taken a winding path to where he is now after signing out of Venezuela in 2011. After pitching for two seasons in the Venezuelan Summer League and one in the Gulf Coast League, Castro underwent Tommy John surgery and missed the 2015 season. He didn't debut in full-season ball until '17, as a 22-year-old in the Midwest League.
From there, Castro has slowly climbed the ranks in the Tigers' organization, topping out at Double-A in 2019, where he posted a 4.40 ERA with 116 strikeouts over 102 1/3 innings. In 2020, Castro made his MLB debut, allowing two earned runs over one inning of work against the Royals.
The appeal of Castro lies in his strikeout ability, which leans heavily on a fastball that sits in the mid-90s but can tick up to 97 mph. He also throws a slider, often as a strikeout pitch, and has a changeup that is still a work in progress.
"When I was catching him, it was pretty easy to catch, because you could always rely on his heater," catcher Jake Rogers told MLB.com back in Spring Training. "It cuts."
Tigers outfielder Derek Hill also offered up a scouting report back in Spring Training after facing Castro and getting a look at his pitches from his spot in center field.
"Everything he throws moves," Hill said. "You could see it from center field, just darting everywhere. If the catcher called three fastballs straight, they'd all do something different. But they'd hit the spot."
Castro's strikeout rate from Double-A in 2019 (10.2 K/9) was his best in the Minor Leagues, but it was offset by an inflated walk rate (5.7 BB/9). While the Blue Jays haven't shared their plans for Castro just yet, all of this information clearly points in the direction of Castro being tried in a relief role, which he's done a handful of times in the Minor Leagues.
The Blue Jays changed their approach to their bullpen in 2020, and while that was mostly a product of the 60-game season, the successes of pitchers like Thomas Hatch, Anthony Kay, Ryan Borucki and Julian Merryweather in multi-inning roles opened some eyes. Shifting to the bullpen -- whether it be temporary or permanent -- is no longer the demotion it once was, and can be particularly valuable if that pitcher is able to sustain velocity over multiple innings.