ST. LOUIS, MO – AUGUST 6: Starter Joe Kelly #56 of the Boston Red Sox pitches against the St. Louis Cardinals in the first inning at Busch Stadium on August 6, 2014 in St. Louis, Missouri. (Photo by Dilip Vishwanat/Getty Images)
It’s only been two games and Joe Kelly has a record of 1-0 with an atrocious ERA of 10.13 in only 8 innings. He has struggled to control his pitches, but there appears to be a trending his approach appearing over the last few seasons to use his slider more. I’m not sure if that has been a great idea and may be partially to blame for his control issues.
Kelly has fluctuated between the rotation and pen over his career and that would play with his approach, but even since he began starting full time since 2014 he’s had a trend to thrown more sliders. In 2014 he threw 6.2 percent sliders and then last season that number jumped to 14.3 percent in his first full season in Boston. He also dropped his high percentage of two seam fastballs for the faster four seam, but has lost some movement on his pitches with that change.
This season in a small sample he continued to throw less two seamers, but instead of more four seamers he’s now thrown 22.5 percent sliders in that sample of 8 innings. It’s not much and it likely will fall, but since coming to Boston he is clearly trying to throw them more, but I’m not sure that the approach he is taking is not making him be worse than he was in St Louis.
Using Pitch f/x we can see how many runs a pitch will be “worth” over an average level. We can then average that over 100 attempts with that pitch and get an idea how good a pitch is compared to each other no matter how often he uses it. In his past two seasons his wSL/c (weighted Slider runs above average per 100 pitches) has been -4.96 and -1.30. That means his slider allows more runs than the average slider for every 100 pitches.
While having a negative value is not a reason not to use a pitch I’d argue it’s a good reason to not use it more. Sometimes you need to use a less valuable pitch to setup hitters so throw a slider to setup a four seam fastball, but do you want to throw another 10% of your pitches as sliders?
So Kelly is throwing more sliders which is not his best pitch. As we discussed earlier he’s also throwing more four seam fastballs, which unfortunately is his second worst pitch based on pitch values/100. In 2014 and 2015 the four seam was valued at -0.63 and -0.85 respectively. The one pitch that Kelly seems to use to good success is his two seam fastball, but it’s the one pitch he has slowly removed from his repertoire.
Part of his usage comes down to what batter he’s facing. Kelly uses sliders and the four seam much more against right handed hitters, but the changeup gets more use against left handed hitters. It’s possible he’s seen more right handed hitters in the American League and that’s why his overall pitch averages have swung, but he’s a better pitcher against righties so that doesn’t seem to be the only change.
In all honesty Kelly struggles to often to throw strikes and with a BB/9 of 3.43 in his career that doesn’t seem likely to change anytime soon. Unlike a high walk pitcher like Craig Kimbrel he doesn’t strikeout nearly enough hitter to make that walk rate acceptable. For some reason the Red Sox continue to hold out hope that Kelly will figure it out, but doing it at the potential cost of major league wins is a bad idea. The best course is to move Kelly to the pen and allow him to build his stuff up for one or two inning chances. As a pitcher who’s K/BB drops from 2.36 the first time through the lineup to 1.35 the next time he would probably make a solid if not pretty good reliever. When Eduardo Rodriguez returns Kelly seems the odd one out and hopefully this is the course the Red Sox take.