Just how good has Storen’s fastball been? According to FanGraphs, Storen’s fastball has been worth 7.2 runs above average, making it the second most valuable pitch this year by a reliever, behind Jonny Venters’s fastball, which has been worth 9.6 runs above average. Last year, over the span of about five months, Storen’s fastball was worth 2.2 runs above average.

Storen feels like he has picked up some velocity on his fastball, but the more likely reason for its effectiveness is location. Last year, Storen’s fastball averaged 94.4 miles per hour. This year, it’s humming at 94.9 mph. The minor difference suggests the improvement owes more to location.

The most surprising difference between this season and last for Storen may be how he’s using his breaking balls. Last year, Storen threw fastballs 60.4 percent of the time. This year, he’s thrown them 65 percent of the time. While throwing more fastballs, Storen is actually throwing more sliders, too – and virtually no curveballs.

Storen is throwing his slider – his most valuable pitch last season, at 4.9 runs above average – 34 percent of the time this year, up from 28.8 percent. Last year, 10 percent of his pitches were curveballs. This year, only one percent have been curves. Storen threw hardly any changeups last year; this year, he has thrown none.

Storen’s success, then, based of the Pitch F/X data sorted by FanGraphs, has been based on better location with his fastball and more reliance on his slider. Pitching coach Steve McCatty has wanted to Storen simplify his approach, and it appears he has – Storen has a full arsenal of pitches, but this year he has more like a two-pitch pitcher, like a classic closer. Whatever he is doing, it’s working.