The Seattle Mariners are sticklers for the new shift rule. As the Mariners faced he Kansas City Royals on Thursday, Royals' second baseman Michael Massey lined up with his heels slightly touching the outfield grass, which is technically illegal with the new rule implemented this season. The Mariners than challenge a routine ground out, and they were successful, meaning Dominic Canzone was safe at first. MLB implemented the new shift rule ahead of the 2025 season, and it's a slight tweak of an already-existing shift rule. The second part of the rule is essentially to prevent infielders from playing in the shallow outfield.