The Current State of Bullpen Usage in 2015

The number of innings a team’s bullpen throws over the course of the season has less to do with the performance of the bullpen than the performance of the starters. Teams with starters pitching deep into games rely less on relievers, leaving the bullpen well-rested and allowing the manager to leverage a team’s best relievers in more important situations. A great bullpen might cause a manager to pull his starter at the first sign of trouble, creating more innings for the bullpen, but for the most part, the starter will pitch as many innings as possible and the rest is left for the bullpen. Once the relievers are called upon, it is the manager’s job to divvy out appearances and prevent overuse. So far this season, the Boston and Tampa Bay rotations have put their bullpens in trouble and St. Louis also appear to be in danger of wearing out their core arms — points which I’ll address momentarily.

First, let’s consider performance. In unsurprising fashion, the Kansas City Royals’ bullpen has produced the lowest ERA among all major-league bullpens in 2015. Their relief corps was a featured strength as the team made it to the World Series last year. From 2012 to 2014, the Royals bullpen WAR of 17.7 is more than two wins greater than the second-place Atlanta Braves, and the bullpen is off to a great start in 2015 (even if their 3.35 FIP does not quite match their sterling 1.56 ERA). The graph below shows every bullpen’s ERA and FIP, sorted by the former.

While the Royals and Cardinals have the best ERAs and solid FIPs, the team with the best FIP so far in 2015 is the Los Angeles Dodgers, who have managed to paper over their lack of rotation depth with an incredible offense and great bullpen. They’ve done a great job building their bullpen for 2015, and despite the largest payroll in Major League Baseball, their bullpen is relatively cheap.

Most of the bullpens’ ERAs outpace their FIPs so far this year, but that is not entirely surprising. Last season was the first year since 2010 that bullpen ERA was not at least one-tenth lower than bullpen FIP league-wde. This season, it is 0.18 lower, but the gap is traditionally wider early in the season and narrows as the season goes on. The Red Sox rotation has received plenty of attention, but the bullpen is not looking great either. Some of the blame should fall on the starters not pitching deep into games, leaving the Red Sox no choice but to use less desirable relievers. Here are the innings totals for teams so far this year.

Tampa Bay has struggled to find starters to give them innings, but the bullpen has thus far stood its ground and provided league average results. Both the Red Sox and the Rays have jettisoned formerly reliable relievers in Edward Mujica and Grant Balfour in an attempt to remake their bullpens early on. The Yankees have piled up a lot of innings, but with Dellin Betances absorbing a lot of innings and free agent signing Andrew Miller also pitching well, the duo has yet to allow a run and both have sub-2.00 FIPs that anchor the Yankees pen. The New York Mets have had the ideal scenario thus far, getting a lot of innings from their starters and solid production from their relievers when called upon.

Innings are not the only way to overwork a bullpen. Putting extra stress on a few arms can have a negative effect, especially when those arms are the best in the pen. Using the best relievers can mask an overall bullpen deficiency, as the results look good. Over the course of a long season, however, teams will have to use all of their relievers for significant innings. Here are the teams with the most multiple-inning appearances so far this season, per Baseball Reference.

Multiple-inning reliever appearances can happen in different situations; a long reliever entering the game in fourth inning is different from asking a high-leverage reliever to get four or more outs late in the game. Dellin Betances and Esmil Rogers represent both sides of that equation for the Yankees. Betances is averaging slightly more than one inning per appearance as a high-leverage reliever while Rogers is averaging almost two innings per appearance, with the team backing off on his usage over the past week or so. Using relievers for more than one inning at a time is not necessarily a bad thing and some of it is a function of failure on the starters as opposed to the bullpen, but of the seven highest teams in that statistic last season, only the Baltimore Orioles posted a sub-4.00 ERA. For the bottom ten teams, only the Milwaukee Brewers and Philadelphia Phillies had ERAs over 4.00 last season.

Pitching out of the bullpen every day can stress relievers and place too much of an emphasis on some relievers at the expense and rust of others. If a manager trusts only a few relievers, he might call on those players too often and wear them out. Below are the leaders in reliever appearances on no rest, per Baseball Reference.

The Cardinals currently have four relievers with at least 15 appearances in Trevor Rosenthal, Seth Maness, Kevin Siegrist, and Matt Belisle while Jordan Walden was already at 12 before hitting the disabled list more than a week ago. While it is possible that all four relievers stay at a roughly 80-game pace the rest of the season, given that just Bryan Shaw hit 80 games as a reliever last year, the Cardinals will have to back off on their reliever use. This is not the first time Mike Matheny has been involved in overworking relievers. Last season, Scott Boras, Rosenthal’s agent, contacted the Cardinals’ organization about their closer’s use after appearing in games on four straight days. There is little correlation between the number of games with no rest and ERA at the end of the season, but the Cardinals are on pace for nearly 200 zero-days-rest appearances when no team had more than Cleveland’s 150 last season.

This early in the year, most relievers are going to have fresh arms. As appearances even out between the relievers over the course of the season, however, some of the production may creep up when teams are forced to turn to their less talented relievers. Conversely, if some of the teams with high innings totals at the moment can get a little more production from their starters, their bullpens could look a lot better when innings are given to those same teams; best relievers. The situation in Boston looks bleak, for example. Without better results from the rotation, the bullpen is not likely to improve. And with regard to the Cardinals, they’ve gotten great production so far, although lesser results are likely in their future.