Yesterday, Jake McGee threw his first inning of 2015. He allowed no hits, and struck out two batters. He threw two curveballs but the main event, as always with McGee, was the fastball.
I won't go so far as to say that Jake McGee has the best fastball in baseball, but it's on the short list. It's one of the hardest fastballs in the league, and it also has a good amount of both rise and run (although the rise is probably a little bit more impressive). There's a reason he can be as good as he is throwing virtually just the one pitch.