Colorado Rockies Add Bullpen Depth with Claim from the Seattle Mariners

The Colorado Rockies make a quiet move, but one that could come to pay off for them down the line in 2026 in the bullpen.

Arkansas Travelers' Blas Castano (16) pitches the ball in a Texas League Championship game against the Amarillo Sod Poodles. | Carter Pirtle for the Amarillo Globe-News / USA TODAY NETWORK

Thus far this season, the Colorado Rockies' pitching staff sits 20th in Major League Baseball in ERA, which is an improvement from how the crew played as a whole last season. A large portion of that lowering of the ERA goes to the bullpen, believe it or not.

As April nears its end, the Rockies' bullpen holds a 3.54 ERA, which ranks them in a 6th-place tie in the National League. Just because the bullpen is succeeding now doesn't mean it will last all season, so the front office made another move to add to the franchise's bullpen depth on Tuesday.

Rockies Add RP Off Waivers from Seattle

Seattle Mariners pitcher Blas Castano poses for a portrait during media day. | Mark J. Rebilas-Imagn Images

As announced by Rockies Club Information on X (formerly Twitter), the franchise added relief pitcher Blas Castaño, who was on waivers from the Seattle Mariners, and optioned him to Triple-A Albuquerque. In response, left-handed pitcher Luis Peralta was designated for assignment.

Castaño made his MLB debut last season after spending seven long seasons in the minors at the age of 26. In that one appearance with the Mariners, Castaño pitched in three innings and allowed three runs on four hits.

He began the 2026 campaign in the minors, and having only been called up once in his career, it made sense for Seattle to make the move. Luckily for the Rockies, his strong start in Triple-A this season might help his case in getting called up to play for Colorado at some point this season.

In six games this year, Castaño holds a 1.42 ERA in 6.1 innings pitched. Sure, it's a small sample size, but Colorado must've been looking at his track record of eight years in the minors as one that they could use in 2026, should a bullpen arm get injured or whatnot.

Seattle Mariners pitcher Blas Castano poses for a portrait during media day. | Mark J. Rebilas-Imagn Images

He holds a 4.44 ERA in his minor league career with 596 innings under his belt. He has experience starting games, coming in for relief, and closing games out, all of which could be beneficial for the Rockies at the major league level.

As for Peralta, the 25-year-old could find his way to another franchise in the MLB, but massive improvements would need to be made. He held a 9.47 ERA with the Rockies in 2025, spanning 22 games and 19 innings, and got off to a 17.18 ERA start in the minor leagues in 2026.

For Colorado, this move is one that can't come back to hurt them, because if Castaño performs well, they got him for nothing.