KC Royals reliever Kelvin Herrera has added a new slider. The addition has turned the formidable set-up man into a full-fledged bullpen beast, but hasn’t made him an asset in fantasy baseball.
Both the Kansas City Star, and analytic site Fangraphs.com, have written extensive articles about Herrera’s new repertoire. There you will hear how Herrera unveiled the new pitch for the Kansas City Royals last October, and is now getting the kind of strikeout rates you’d expect from a guy whose fastball can touch 100 mph.
Kansas City Star beat writer Rustin Dodd’s research showed that the new pitch has entirely changed Herrera’s pitch mix:
"A brief glance at advanced pitching data illustrates the difference. According to numbers from FanGraphs.com, Herrera used his fastball 83.5 percent of the time in 2015 and more than 78 percent for his career. This season, Herrera has thrown a fastball just 56.6 percent of the time, turning to his slider 19.3 percent of the time. He is still throwing change-ups nearly 16 percent of the time, which correlates with his career averages. But the slider has transformed what he can do on a mound."
Jeff Sullivan’s piece at Fangraphs.com used video to show how the new weapon affects hitters at the plate, calling the upgraded Herrera virtually unhittable.
However, to me, the most telling information comes from digging into Kelvin Herrera’s whiff rates on Brooks Baseball. Not only has the new pitch given Herrera a new weapon, it’s drastically increased the swing-and-miss rates on his OTHER two pitches: namely the fourseam fastball and change-up: