Joba Chamberlain's slider shows he fatigued late in 2014 season

On Tuesday morning, general manager Dave Dombrowski announced that the Tigers had re-signed free agent right-handed pitcher Joba Chamberlain to a one year, $1 million contract. In 2014, Chamberlain was the eighth inning man and Detroit's most consistent bullpen performer for half the season, but fell apart for the remainder of the year around the time of the All-Star break.

Known for his beard of epic proportions and his tendency to throw lots of breaking balls, Joba got knocked around quite a bit as the season unfolded. In the first half of the season, he threw 37 2/3 innings compiling a 2.63 ERA, a 2.47 FIP, 9.56 strikeouts per nine innings, 2.87 walks per nine innings, and a .268 wOBA against. Chamberlain did a complete 180 in the second half, where he threw 25 1/3 innings posting a 4.97 ERA, a 4.20 FIP,  6.75 strikeouts per nine innings, 4.26 walks per nine innings, and a .320 wOBA against. Overuse of the breaking ball from the start could have been a problem, along with natural regression to the mean, but that doesn't do justice to the full story.

A large part of the problem was the fact that Chamberlain's breaking balls got worse as the year went on.

First, let's take a look at Joba's pitch usage throughout the season. Brooks Baseball tracked Joba throwing five types of pitches in 2014, a four-seam fastball, curveball, slider, changeup, and sinker. Considering he only used three of those five pitches consistently, the changeup and sinker have been omitted from the data.

The use of each pitch changed month to month, but there were really no changes in trends. The major constant throughout the season, including the small sample size of the playoffs, was that Chamberlain threw more breaking balls than fastballs. Joba can throw 95 miles per hour, so it's odd that he didn't put his four-seamer to work more often. The next two charts show the change in horizontal and vertical movement in his breaking balls, and I can promise you that there will be a noticeable difference.

To sum up both of the movement charts, Chamberlain's breaking balls were moving much more during the months of April, May, and June than they were in July through the end of the season. Baseball is a game of inches, so even the slightest differences can change what a hitter does with the pitch. It's pretty clear to see that horizontally both his curveball and slider started to move less as the season went on, but the vertical movement chart is a little harder to understand.

Both charts track the movement of a baseball relative to a ball thrown with zero spin. Joba's slider never had a whole lot of vertical movement, but by the end of the season was not breaking as sharply. In the playoffs, his slider flattened out even more. His curveball, which started out as a devastating pitch, also suffered, and broke less as his workload piled up.

Moving Forward

The 2014 season was the first of Chamberlain's career where he used his fastball less than half the time. My theory on why he dilapidated as the season progressed is that he was fatigued by all of the stress put on his elbow. A victim of Tommy John surgery in June of 2011, he might not be physically able to continue throwing breaking balls at the rate he did last year, whether he consciously realizes it or not.

In my eyes, the best way for the Tigers to keep Chamberlain useful for the full length of the season is to lessen his role at the back end of the bullpen. Obviously there's no guarantee that less usage will solve his issues, but based off the data on his breaking balls, it's a theory worth testing.

Bringing back Chamberlain was a good move by the Detroit brass. For the first half of the season he was one of the most dominant bullpen pitchers in Major League Baseball, he just seemed to run out of steam towards the end. With a full year of Joakim Soria, a healthy Bruce Rondon, and (hopefully) a bounce back year from Joe Nathan, Brad Ausmus will have other arms at his disposal than just Joba Chamberlain.