Basically, none of his stuff is even MLB average.
Right now, he throws in the high 80s, topping out around 91. Just knowing that, you'd think Sewald is a finesse-pitching control artist. You'd be absolutely right. Sewald can spot his heater on both sides of the plate, and he doesn't walk many. But what's probably helped Sewald the most this season was his decision to scrap his ineffective slow curve in favor of a tighter high-70s slider, which has been a little more effective at getting hitters to swing and miss, elevating him from pure organizational fodder to someone with at least a chance of pitching his way into the back end of a big league bullpen. He also adds a changeup which is fringe-average.