. For his career, Perez has struck out a mere 13.9% of opposing batters.
True.However one needs to get a bit more granular with that.He has struck out 20.7% with his changeup and 21.8% with his slider (career numbers).His sinker induces 60.4% ground ball rate.
Those are not bad numbers, esp. for a back of the rotation guy.
His problem is his four seamer and curve that are pretty awful.Last season opponents hit .422 off his four seamer (vs. 286 off his sinker) and 37.5% of the flyballs off his curve were home runs (that moved his overall to 18.2%).Getting rid of those pitches that he threw 25% of the time will go a long way towards improvement.
If one can see that opportunity by simply looking at publicly available numbers, I am sure that the Twins saw even more, because they have more data.