Brandon League of the Seattle Mariners earned an All-Star berth as he experience the best season of his short career. League brought down both his walk rate and home run rate this season leading to a career best .268 wOBA. Weighted OBA represents linear weights put on the scale of OBP, so league average is going to be around .330. This season, when batters face Brandon, they are hitting below replacement level.
During the previous three seasons, League induced batters to swing at pitches off the edge of the plate on the catcher's glove had side.
Batters expanded their strike zones. League used to get a fair amount of called strikes there, as batters defined a wider zone:
This season, he's getting a much wider slice off the plate.
Where he used to get some yellow up to the dotted line, (the could go either way part of the strike zone), he's now getting some red past it. That's nothing but good for Brandon. If batters take the pitches, (which they should), the called strike puts them in a hole. If they swing, it's not a good part of the strike zone in which to make solid contact. As long as League continues to get these calls, he'll have the advantage over the hitters.