I didn't really follow baseball in 2020, was he injured ?
He's been banged up and also not playing terribly well when he did. He's still plenty young enough to bounce back though.
One thing I read said baseball people think he started swinging for the fences too much. I can't imagine that happens in the K.
Yes, he did get hurt last year. I don't buy the swinging for the fences narrative at all, in fact this is the first time I've heard that. If that was his issue, I don't know why hitting at The K would make a difference, Fenway isn't more hitter friendly, especially for lefties, it goes from 420 center to 380 in the right field power alley.
His plate discipline is also good. It was good when he was taking and actually got better during his slump, his walk rate went from 8% to 12%.
The theory I've read that makes the most sense is that his bat speed has slowed down, if that's what happened it's recoverable, he's still a young kid, far from washed.