Masterson brings up a good point. One thing he is definitely doing differently is throwing more four-seam fastballs this year to mix in with the two-seamer. If pitching is about disrupting a hitter's timing, Masterson is doing it with a harder four-seam fastball with less movement to play off his sinker rather than using a changeup, and the addition of more four-seamers has made him more consistently effective thus far. So he is changing speeds more this year, just in a different way than expected.
— A Jason Grey piece over at ESPN (Insider, I think) about the Big Masty's success this year.