Joe Kelly has pitched for the Red Sox for 2 ½ seasons now, and has mostly been a mediocre starter in spite of his tremendous stuff. In 2016, he opened the season as a starter, but put up terrible numbers (8.46 ERA, 2.26 WHIP in 22 1/3 innings) and was sent to the minors after six starts. In July, he was brought back to the big leagues, this time as a reliever, and was pretty spectacular (1.02 ERA, 1.05 WHIP in 17 ⅔ innings), finishing up with 3 ⅔ perfect innings in the postseason. The plan for 2017 is to keep Kelly in the bullpen.
Kelly’s sample of pitches in 2016 was small, both as a starter and a reliever, so take these charts with a grain of small-sample-size salt. As a starter, Kelly threw a fastball (“FF”), slider (“SL”), curve (“CU”), and changeup (“CH”). His fastball as a starter covered a wide range of velocities, and probably included both a two-seam and four-seam variety, but if he did, there is no clear distinction between them and I am just calling everything a four-seam here:
As a reliever, Kelly dropped the changeup, but kept the other three pitches. (In this chart, I pooled Kelly’s regular-season and postseason relief appearances to increase the sample size a little.)
Kelly threw his fastball just over 60% of the time, both as a starter and reliever, with his curve and slider roughly splitting the rest. As a starter, Kelly threw his changeup mostly to left-handed batters; he didn’t throw it at all as a reliever. (Again, the reliever chart combines his regular and postseason appearances.)
Unsurprisingly, as well as being more effective overall as a reliever, most of Kelly’s pitches were more effective in relief:
His fastball went from worse than average to significantly better in total bases per pitch, and also improved in strike percentage. His curve was effective, both as a starter and in relief. His slider effectiveness changed drastically, going from slightly worse than average to extremely effective. His worst pitch was his changeup, and simply dropping this pitch altogether as a reliever helped to improve his results.
It’s common for pitchers to throw harder in relief than as starters, and even though Kelly was one of the hardest throwing pitchers in baseball as a starter, he still managed to find another gear as a reliever, increasing his average fastball velocity from 95.7 mph as a starter to 98.8 as a reliever. This chart compares his fastball velocity and movement to that of other right-handed pitchers (limited to those who threw more than 100 fastballs in the season). Kelly’s fastball as a starter is colored blue, as a reliever (including the postseason) in red:
As a reliever, Kelly threw faster than all but one other right-handed pitcher (Mauricio Cabrera, who clocked in at an average of 100.5 mph); Noah Syndergaard was just behind Kelly at 98.5 mph. As these charts show, Kelly sacrificed some horizontal movement for speed, but his fastball already had fairly extreme movement, so even his faster pitches in relief were in the usual range for fastballs.
We can look at the movement and velocity for all of Kelly’s pitches, as a starter, in relief during the regular season, and in the postseason (though, remember, in a total of just 3 ⅔ post-season innings). Here the dots are sized proportionately to the number of pitches thrown:
Note first how all of his pitches became faster when he converted to relief, generally without sacrificing movement to any extent. Also, particularly note the change in his slider (the purple dots) in the postseason. Kelly commented that he changed the grip on his slider in the postseason and was very happy with the results. However, it seems from these charts that his new grip both increased the speed and reduced the movement on the pitch, making it more fastball-like and less curve-like — in other words, more like a cutter. It will be interesting to see if he continues to use this pitch in 2017, and if it continues its effectiveness as batters learn to expect it.
In any case, there are clearly significant changes in the velocity and movement of Kelly’s pitches that correlate with his success as a reliever. With the acquisition of Chris Sale in the offseason, there is probably no place for Kelly in the rotation, but both the team and the fans hope he can continue to be effective out of the bullpen and contribute to the team that way. Perhaps he can become the Red Sox version of Andrew Miller.