Touching BasesMarch 18, 2010
Kevin Jepsen: Sleeper
By Jeremy Greenhouse

He's got Brian Wilson's fastball/slider combo plus A.J. Burnett's curve. Kevin Jepsen's stuff is that good.

I first noticed Jepsen when he topped my "Stuff" leaderboard back in September. He had only thrown 330 pitches on the year at that point, so I didn't make much of it, but the numbers ranked him right up there with Wilson.

He then burst upon my radar in the ALCS last year when his stuff blew away a couple Yankees as well as Carson Cistulli and myself. In 2002, Francisco Rodriguez was the Halo rookie who made waves in the playoffs. In 2008, Jose Arredondo captured some of that K-Rod magic. Now I'm not saying Jepsen will have the subsequent success of K-Rod or the sophomore slide of Arredondo. But I'm thinking he's closer to the former than the latter.

Jepsen had allowed 5.4 walks per nine innings before being called up to the Majors in 2008. Since then, he's proven that he can harness his electric stuff in 63 regular season innings. His career MLB BB/9 is 3.3, better than both Wilson's and Burnett's. His strikeout rate has been somewhat lower than expected, though at nearly eight Ks per nine, it's nothing to sneeze at. Kept the ball on the ground? Check. Career 55% ground ball rate. So what's with that glaring 4.86 ERA that's holding him back from being widely regarded as a potential breakout candidate in 2010? A .360 BABIP and 61.9% strand rate. Gotta love it when bad-luck indicators line up like that. Jepsen's career 2.86 FIP is a full two runs lower than his ERA. In the last two years, Damaso Marte's ERA-FIP of 1.32 is the next closest to Jepsen's among relievers with at least 60 innings pitched.

PECOTA and ZiPS project Jepsen for an earned run average well north of five. CHONE is more bullish, projecting an ERA of 4.14. Still, every projection system forecasts major regression in 2010 from last year, which is fair, considering he has outperformed in MLB compared to his Minor League numbers. Why should you believe that Jepsen can continue to outdo his pre-2008 track record?

On the PITCHf/x front, The Orange County Register's Sam Miller's got you covered. The whole article is worth a read, but allow me to quote heavily from it.

Here’s what changed:

The first photo shows Jepsen’s pitch movement (from the catcher’s perspective) in April and June. The second one is his pitch movement from July 1 on.

In the first photo, Jepsen basically has two pitches — a fastball that usually bores in on righties, and a curveball with downward movement. In the second photo, allllll that space in between them is filled with the green pitch. It’s labeled a slider, and it behaves like a hard slider — 89 mph, with movement away from the right-hander — but is perhaps best called a cutter. The LA Times quoted the Angels as saying it’s a cutter that Mike Butcher taught Jepsen in early July. Later in the season, Jepsen seems to refer to it as his slider. Cutters and sliders aren’t that different, and the label isn’t as important as how well it worked.

When hitters swung at it from Aug. 1 on, they got nothing but air 55 percent of the time. Zack Greinke’s slider might be the best in the game, and he got whiffs on 42 percent of swings. Frankie Rodriguez gets whiffs on 28 percent. Billy Wagner, 37 percent. Mariano Rivera’s cutter: 25 percent. It was, for Jepsen, a massively good pitch. (Here’s a not-very-good example of it.)

There's not really much to add to that. Miller concludes that Jepsen "now projects as a possible future closer. Maybe by the end of this year." I'm inclined to agree. Brian Fuentes wavered down the stretch last season, which cast a seed of doubt in manager Mike Scioscia's mind. Pre-All-Star break, Fuentes added 1.4 WPA, but from the midsummer classic on, he lost -0.5 WPA.

"Both guys have been an important part of the back end of the bullpen," Scioscia told Brittany Ghiroli in mid-September. "But if there are some matches that could be advantageous [to use Jepsen], we will try to take advantage of [them]."

Fuentes had the lowest fastball velocity of his career since he inherited the Closer role. His 19.7% whiff rate fell well short of his 26.4% career average. He also threw only 47.7% of his pitches in the strike zone compared to a 51.95% career rate. While Jepsen's FIP has fallen short of his ERA, Fuentes pitched to better results than his peripherals would suggest. His tentative hold on the ninth inning job is slipping. If you're playing fantasy baseball, I doubt you'd even need to draft Kevin Jepsen to own him. But be ready to scoop him up off the waiver wire, because I have a feeling that once the season starts and he gets another chance to show everybody his stuff, he's going to pick up helium.



Comparing the walk percentages for a starter and a reliever really can't be done straight up. It's been shown, quite clearly before, that the average starter that has pitched in relief has a higher K rate and lower BB rate in as a reliever.

Also, the article that you quote talks about Jepsen getting swing and misses on 55% of his cutter/sliders.. but according to Fangraphs that's a total of around 238 pitches in his career. I'm willing to wager that we need a higher number of pitches before the swing and miss percentage for that type of pitch is reliable. I'm willing to bet there will be some regression to the mean in terms of contact on his slider/cutter, even.

Finally, don't forget that the Angels have Fernando Rodney locked up for a fair amount of money and would likely turn to him first to close.

I'm a big fan of Kevin Jepsen, as I've mentioned here before. When he added the slider in the middle of last year, he cut way back on his curveball usage and became a much better pitcher.

I think most people don't realize this because he was so poor earlier in the year, due to still getting over back trouble during April, and then being mediocre after that until he debuted the slider on July 3.

@Adam B, I haven't done a detailed study, but I would wager that whiff percentage on a given pitch type stabilizes very quickly, and that a couple hundred pitches is already a good sample size for that.

Adam, I think you're misinformed. Tango just wrote about the rule of 17 last week.

"Basically, use the “rule of 17”: difference in BABIP is 17 points higher as starter. K/PA is 17% higher as reliever. And HR per contacted PA is 17% higher as starter. Walk rate is FLAT."

You're right that to determine a stable whiff rate, we need a whole lot of pitches. But using the StuffRV numbers I use, we only need a few. That pitch is excellent no matter how you look at it.

I did forget about Rodney, of whom which Rich Lederer also reminded me. Still, Jepsen might be better than him, too.

Sorry, couldn't remember the study off the top of my head. And I'm not denyiung that it's going to be an excellent pitcher, just that the whiff rate of it may regress. Doesn't mean there will be good contact on it at all.

Hey Jeremy. What's the difference in Jespen's stuffRV before and after he added the slider/cutter?