I realize that analysis of Kansas City Royals relievers don’t make for the most appealing of baseball blog posts, but this piece from Baseball Prospectus is one of the more interesting articles I’ve read today. Mike Fast takes an in depth (emphasis on depth) look at Joakim Soria’s recorded velocity over the last few years, and debunks the myth that his struggles so far this season are a result of diminished speed.

The appropriately named Fast instead finds that Soria’s dip in velocity is due to a combination of changes in the calibration of Kaufman Stadium’s pitch speed measurement system and the development of a new, slower and more cutting pitch.

So Soria has a new pitch? Yes, and it has apparently turned him from a strikeout artist into a groundball machine. Prior to the introduction of the slower cutter, about 40 percent of his balls in play were on the ground. Since then, 51 percent of his balls in play have been grounders.

Fast examines Soria’s Pitch FX charts to note the exact date in which the Royals closer began using his new pitch.

Soria introduced the slower cutter on July 29, 2010; since then, he has had a swinging strike rate of only 6.8 percent on his fastballs, but his results on balls in play have improved markedly. His swinging strike rate has dropped primarily because the slower cutter is not a swing-and-miss pitch. Since introducing the slower cutter, he has gotten whiffs on nine percent of his faster fastballs and five percent of his slower cutters. He has traded whiffs for groundballs and avoidance of the home run.

However, that doesn’t explain his struggles so far this season. While it’s still too early to truly get worked up about a lack of results, Fast does mention that Soria’s curveball, which used to be his out pitch, has been on the decline since the end of 2008. He goes on to speculate that the development of the new ground ball inducing pitch is likely a result of this decline.

It’s really fascinating work from one of the more clever analysts out there. If you’re interested in more of this type of work, I’d encourage you to follow him on Twitter.