Kevin Jepsen’s new arm slot: productive or problematic?

kevin jepsen angels

Stuart Wallace is an associate managing editor and writer at Beyond The Box Score. You can follow him on Twitter at @TClippardsSpecs.

One of the more tangible changes seen out of the Los Angeles Angels of Anaheim bullpen involved Kevin Jepsen lowering his arm slot from an over-the-top to a low three-quarter release point. It was a calculated move by Jepsen, done not only to streamline his mechanics in order to have a more natural arm angle that would help keep injury and pain at bay, but also to improve his curveball, giving it more bite and movement and allowing him to scrap a cut fastball that had provided inconsistent results.

Between Jepsen himself calling the curve with his new delivery “nasty” and catcher Chris Iannetta applauding the reliever’s consistency with the lower arm slot and improved breaking ball, all signs pointed to Jepsen’s change to be for the best.

So what does the new Jepsen look like from a PITCHf/x perspective and has the change reaped the benefits Jepsen and the Angels had hoped?

First, a quick look at the horizontal and vertical changes to Jepsen’s release point—on the left is his release point up until this season and on the right, the new release point for 2014:

kevin jepsen pitch frequency chart
(Click to enlarge)

Reviewing the x-axis and the horizontal aspects of the release point, we see Jepsen roughly half a foot further away from his body with the new arm slot; as far as the vertical component (y-axis) is concerned, we see less dramatic shifts in the release point, but do find Jepsen releasing the ball a little lower than in previous seasons, with no pitches over six feet in release height.

Let’s shift focus to the curve—has it been as nasty as Jepsen purported before the season started? In the table below is a small selection of stats describing the breaking ball before and after the arm slot tweak to see if there has been an appreciable change in the pitch:

Kevin jepsen chart

So far, it appears the new and improved curveball for Jepsen has just been ‘new’—drops in ground balls, strikes and whiffs concomitantly with increases in swings, line drives, and extra base hits (as judged by ISO) have plagued Jepsen’s breaker. Using the PITCHf/x pitch values per 100 pitches statistic as further comparison shows the 2014 version of the curve coming in at -1.15,  a striking drop from his 2013 pitch value of 1.62. In the small sample of this season, the breaking ball for Jepsen has appeared to have lost some its bite.

Regarding Iannetta’s comment that Jepsen’s was throwing the pitch more consistently for strikes, let’s take a look at Jepsen’s strike zone heatmap. On the left is the heatmap for all curves prior to 2014, with the heat map on the right showing us 2014 curves:

Kevin Jepsen heat map (Click to enlarge)

Despite a rough showing with the pitch outcome-wise, we do see Jepsen doing a better job of burying the curve down in the zone and less likely to flip one up in the zone.

Overall, the results have been less than desired for Jepsen with the new arm slot and curve ball. Breaking down the data further and looking at left-right splits and we see another aspect of the new arm slot hurting Jepsen’s productivity thus far. Over his career, Jepsen has done a great job of getting righthanded batter outs, enjoying a .283 wOBA; lefties have given him fits in general, hitting at a .342 wOBA. With the new arm angle, Jepsen has the added benefit of increased deception against righties, with pitches now coming out of his hand almost behind righthanded batters; unfortunately, at bats for lefties aren’t as uncomfortable, with the more horizontal angle giving lefties a better look at the pitch as it comes toward the plate. This has led to righties hitting at a .275 wOBA, versus a .362 wOBA against lefties, in 2014, an almost three percent improvement in wOBA against righties, but a near six percent drop in effectiveness against lefties.

While there is still time for Jepsen to hit his stride with the new arm angle, it appears that lefties could continue to feast on pitches out of this low three-quarter slot, as they now have even more time to read and react to pitches. Looking at Jepsen’s horizontal and vertical release point components across this season on a game-by-game basis, we see Jepsen’s release point starting to creep back up to pre-2014 values, perhaps in response to the teething problems seen with the more sidearm slot.

First, horizontal:

kevin jepsen horizontal release point 2014

…and here, vertical release point trends:

kevin jepsen vertical release point

While the horizontal aspects of his tweaks are most affected, we still see Jepsen’s release point still being a work in progress. With a -1.89 RE24 and a 4.22 FIP (compared to a 3.26 xFIP) so far in 2014, the talented flamethrower’s new look could be all for naught if he continues to struggle both with mechanics and getting hitters out on a consistent basis.