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Welcome to the new era of bullpens

Bullpens are used now more than ever, but how effective is the strategy?

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Miami Marlins v Arizona Diamondbacks Photo by Jennifer Stewart/Getty Images

Bullpens are more heavily used now than they’ve every been before. That’s not news to most people who follow baseball given all the talk around limiting pitch counts and workloads in effort to keep starters more healthy and more effective. Bullpens are now more important than ever. With the increase in importance the one thing teams need more than ever is quality relievers who can keep the game where it is once the starter exits. That’s something obvious but it becomes all the more necessary when bullpens play a bigger role in how the game plays out than in prior years.

What is surprising though is how the game shifts and adjusts to the changes in bullpen usage. You see batters who are okay with striking out swinging more often because they know they can’t afford to take too many pitches; they have to make something big happen and the only way to really do that is to swing. You’re also seeing relievers who are okay with giving up a hit or a walk if it means they can escape the inning without allowing a run. They’ll surrender a single to a Mike Trout or Bryce Harper to get to someone with less offensive skills in order to ensure no runs score.

In order to more effectively show how the bullpen usage is changing, I went ahead and charted some important pitching metrics league-wide over the past ten seasons. I included 2018, left the averages the same but extrapolated the totals, like innings, using 2017’s totals, in effort to show where the numbers would finish this season with the current pace.

Bullpen League Averages

Year G IP K% BB% ERA SIERA FIP fWAR SwStr% W/L% LOB% .AVG BABIP
Year G IP K% BB% ERA SIERA FIP fWAR SwStr% W/L% LOB% .AVG BABIP
2018* 15657 16984.2 23.5% 9.3% 3.88 3.69 3.86 117.3 11.5% .515 74.0% .239 .296
2017 15657 16469.2 23.3% 9.2% 4.15 3.95 4.16 112.7 11.6% .519 73.5% .242 .295
2016 15303 15893.2 22.7% 9.0% 3.93 3.80 3.99 103.3 11.1% .526 74.0% .243 .296
2015 15106 15184.1 22.1% 8.6% 3.71 3.58 3.83 87.1 11.0% .511 74.1% .241 .294
2014 14460 14621.2 22.2% 8.7% 3.58 3.34 3.60 84.7 10.6% .505 73.9% .238 .294
2013 14336 14977.0 21.7% 8.9% 3.59 3.46 3.70 93.2 10.5% .504 75.2% .239 .291
2012 14524 14737.2 21.9% 9.1% 3.67 3.60 3.79 97.9 10.2% .517 74.5% .239 .291
2011 13893 14228.0 20.6% 9.4% 3.69 3.56 3.83 75.6 9.7% .504 74.3% .239 .287
2010 13926 14244.1 20.3% 9.6% 3.93 3.69 3.99 73.7 9.6% .506 73.5% .245 .294
2009 14237 15014.2 19.5% 10.1% 4.08 3.98 4.21 79.9 9.5% .503 73.3% .247 .292
*2018 was averaged with 2017's game numbers

As you can see, bullpens are getting more swings and misses, striking more guys out, and leaving more men on base despite a batting average against that is around the same as it’s been the last decade. As a result they’re winning more games than previous seasons which is exactly what teams are looking for when constructing their bullpens.

However it should be noted that the league is beginning to adjust to the “bullpenning” that has been occurring the last few years. First, the walk rate is steadily increasing, as batters are taking more pitches and forcing relievers to locate their pitches more effectively. Second, the number of runs relievers are giving up is steadily increasing as well. Batters are doing everything they can to score off relievers—that hasn’t changed—but with the fly ball revolution and the death of the small-ball baseball, teams are putting late rallies together quite often.

Another way to see the trend is when looking at the average innings pitched per start. I charted the league-wide average number of innings pitched per start by starters. In order to best compare the seasons, I left the initial result without converting the decimal into third’s as well as converted them, that way you can see exactly how much it is changing.

Starter League Averages

Year Raw IP/S IP/S
Year Raw IP/S IP/S
2018 5.48 5.1
2017 5.51 5.2
2016 5.65 5.2
2015 5.81 5.2
2014 5.97 6
2013 5.90 6
2012 5.89 6
2011 6.03 6
2010 5.98 6
2009 5.81 6

Just five years ago starters we’re averaging six innings per start, which means many of them went deeper than that. This year is the first year where the average was below five and two-thirds innings. This is one trend that surely will continue, as teams are developing strategies both on and off the field to form the best bullpens possible.

The 90’s and early 2000’s saw the storied rise of great closers like Mariano Rivera and Trevor Hoffman. Since then we’ve seen the rise of great setup men like Andrew Miller, Koji Uehara and more recently Dellin Betances.

Now we’re seeing those in-between’ers the guys that come in to bridge an inning-plus to get to those setup men and closers. Some names that come to mind are guys like Chris Devenski, Josh Hader, and Blake Treinen. These relievers are ushering in a new era of the bullpen. When starters are coming out in the fifth inning as opposed to the sixth it only adds to the number of outs the bullpen has to earn.

Not only are we seeing a rise in the number of relief pitchers who pitch more than three outs, we’re also seeing a large increase in the number of relievers who pitch less than three outs. Managers have experimented with different approaches and strategies to see what works and we’re seeing both multi-inning relievers and less-than-an-inning relievers being heavily used in today’s game. We’ve even for the first time seen a strategy tested where a reliever “opens” the game and then a starter or long reliever comes in after an inning.

These experiments are no doubt eye-catching and often fun to watch develop. As these experiments continue we’ll see some that work and some that don’t. Without question teams will be more willing now than ever to pay more for quality relievers when they’re used almost just as much each game as starters.


Ron Wolschleger is a pitchaholic and a Contributing Writer for Beyond the Box Score as well as Bless You Boys. You can follow him on Twitter at @FIPmyWHIP.