The Opener: Mariners, Henderson, Minor Leagues

As the 2025 regular season continues, here are three things we’ll be keeping an eye on around the baseball world throughout the day today:

1. Mariners 40-man move incoming:

The Mariners are reportedly poised to select the contract Luis F. Castillo today, who will start today’s game against the Giants and Justin Verlander after teammate and veteran righty Luis Castillo started the club’s last game on Wednesday. In order to make way for that quirky bit of trivia, Seattle will need to clear a 40-man roster spot. With no obvious candidates for the 60-day injured list on the roster, the Mariners will likely need to designate one of their players for assignment, at which point they’ll have one week to either trade that player or successfully pass them through waivers.

2. Henderson likely to be activated:

Gunnar Henderson opened the season on the injured list, but manager Brandon Hyde told reporters (including Andy Kostka of The Baltimore Banner) that it’s “probable” the star infielder will be activated from the injured list to start the club’s series opener against the Royals in Kansas City, for which Baltimore will be facing veteran right-hander Seth Lugo coming off his dominant 2024 season where he finished as the runner up to Tarik Skubal in AL Cy Young award voting. The Orioles have gotten off to a difficult 3-4 start to this point in the season, but the return of Henderson after a year where he broke out to the tune of a .281/.364/.529 slash line and finished fourth in AL MVP voting should go a long way to improving the club’s offense. The return of Henderson figures to kick Jackson Holliday off shortstop back to second base, with Jordan Westburg returning to third base after covering the keystone and Ramon Urias heading for the bench.

3. Minor League Opening Day:

While the major leagues had their Opening Day last week and Triple-A followed suit shortly there after, the rest of minor league baseball has not yet began their seasons. That changes today with the arrival of Opening Day for Double-A, High-A, and Single-A affiliates all around baseball. The earliest of those games is a game between the Double-A affiliates of the Orioles and Pirates, the Chesapeake Baysox and the Altoona Curve. That game begins at 5pm CT this evening, though of course all three levels have 15 games scheduled to run throughout the evening. Prospect hounds will get their first opportunities to catch glimpses of the 51 of MLB.com’s Top 100 prospects who are currently in the lower full-season levels of the minors, including top-ten talents like Twins outfield prospect Walker Jenkins, Tigers outfield prospect Max Clark, and Guardians second base prospect Travis Bazzana.