All week I’ve been working on a way to accurately rank the bullpens across the league. It was by no means an easy task. There are so many different ways to look at a relief corp. Some bullpens win a lot of games, while others seem to allow very few runners. Still others don’t give up many runs, but maybe that’s due more to a fantastic defensive effort. I looked at the metrics that have a high impact on pitcher success and then compared that to what has been league average thus far in a young 2018 season. I selected five stats that I felt carried the most weight in accurately judging the overall strength of any given bullpen.
A reliever with a high strikeout rate is incredibly valuable to his team for a couple reasons. There is the obvious advantage of allowing less balls in play, therefore less chances of a hit. Then there is the advantage of reducing the opponents opportunity for situational hitting. Let’s say team A has a runner on second base with no outs in the eighth inning of a tie game. Team B brings in their bullpen ace to close out the inning. That ace gives up a ground out to second for out number one and the runner moves up to third. Then our ace gives up a fly out to medium deep left center and the run scores on a sac fly. Without giving up a hit, team B lost the lead. Now, if our ace was able to get a strikeout on either of the first two hitters, team A needs a hit/error to bring in the run. The strikeout eliminated the ability of team A to utilize situational hitting to manufacture that run. Given the high leverage situations often faced by relievers, the strikeout becomes a vital tool for success.
This is simply the percent of balls in play that are ground balls. The league is slashing .235/.235/.256 on ground balls thus far in 2018; compare that to .385/.379/..725 on balls in the air. The more ground balls a pitcher can induce, the less chances the opponent has to get guys on base and to drive guys in. Pichers that keep the ball on the ground more than 48% of the time are vital to their bullpens success.
The advantages of this metric should be fairly obvious. This is the number of runners a reliever strands on base. Most pitchers tend to hover around league average in LOB%, which was 72.6% in 2017, but pitchers that record a high volume of strikeouts tend to be better at stranding base runners.
This stat needs a little more explination. Like many of the ERA estimators, SIERA tries to give us a picture of what the pitcher was able to do seperate from his defense. It tries to isolate the pitchers performance and hold it under a microscope. Just like stats like FIP, SIERA looks at walks, strikeouts, and home runs, but it goes beyond that to look at balls in play as well. It attempts to figure out what balls in play are influenced by the pitcher, and filter out the balls in play that are influenced largely by his defense. It it a nice tool to get a look at a more complete view of a pitchers individual performance.
Now a well known metric, WAR was once a new age, controversial stat. This early in the season nearly every bullpen in the league is going to be within 1 WAR from top to bottom. This is more of a counting stat that will become more useful as the season wares on.
The following chart shows the ranking and statistics of every bullpen in baseball. It’s color coded to show that blue is the top five performers in their category, yellow is the next five, and red is the bottom five.
The Astros graded out as the top bullpen in baseball. They top the list on the back of fine early performances from Hector Rondon (12.6 K/9, 0.00 ERA), Brad Peacock (12.4 K/9, 100% LOB), Chris Devenski (10.5 K/9, 65% GB), and Collin McHugh (13.5 K/9, 60% GB). The Brewers and the Cub are right on their heels, with the Padres pen rounding out the top five. Close behind those are the Indians, Yankees, Giants, and DBacks, all with very strong bullpens.
The bottom of our list we find the lowly Pittsburgh Pirates. They unquestionably have the worst bullpen in baseball. The Bucks don’t have a single reliever with all around good skills. The closest is Tyler Glasnow who has fine peripherals with a 13.5 K/9 and a league average 47% GB rate, but his 6.75 ERA throws a monkey wrench into the whole deal. He does have a very high .353 BABIP, which is one reason why his FIB is a low 2.30 suggesting that his poor ERA is more the results of bad luck.
Beyond the Pirates, the Royals, Rays, and Reds are right there at the bottom with just terrible pens. These four teams are just on another level of bad. The Marlins round out the bottom five of this list.
We will be doing more on bullpens as the season goes on so stay tuned for more up-to-date rankings. It will be interesting to see how things play out these teams log more innings out of their relievers.