He attempted to throw out a runner in the 3rd I believe, he finished the inning behind the plate, but then Hill was back out there the next inning and they said he left with shoulder tightness/pain from attempting to throw the runner out. I would guess this early in the year it's more precautionary than anything, but you know it's the Cubs... Not to nitpick, but your original wording implied that the runner was unsuccessful in stealing against Soto, who was working in very mysterious ways last night. Also, IIRC, he stuck around another couple innings and even batted again before being lifted.