The Houston Astros' outstanding bullpen

The first place Astros owe their first placeness primarily to pitching. The offense’s roughly league average 99 wRC+ is good for only eighth in the American League. That’s not bad, but it’s not what’s propping up the team’s 29-16 record. Rather, the pitching staff’s 88 ERA-, second in the AL, has been a bigger reason for the team’s excellent start. The bullpen has contributed significantly to that success. The bullpen has not just been good, either. It’s been great. In fact, it might end up as the best bullpen in baseball in 2015. Let’s ask three fundamental questions about the bullpen.

How good are they?

Very good. Through Sunday's game, Astros relievers have combined for a 2.14 ERA and an ERA- of 54 in 2015, both of which are second only to the Royals. The committee’s 2.89 FIP is third in baseball, but this time they are behind the Dodgers and Marlins. If run estimators are your preferred flavor, the Astros’ bullpen leads all of Major League Baseball with a 2.90 xFIP and a 2.41 SIERA, according to FanGraphs. A lot of attention is given to the preternatural Royals’ bullpen, and while that squad has a 1.68 ERA to show for itself, they actually lag quite a bit behind the Astros and other teams when it comes to xFIP and SIERA. The Royals bullpen ranks 13th in xFIP and 14th in SIERA.

The Astros are more convincing to the run estimators because they are excelling in striking batters out and limiting walks. The Astros’ bullpen has a 28.9 percent strikeout rate, which is behind only the Dodgers’ bullpen. Their 6.0 percent walk rate is the best in baseball. Couple those bits of performance, and the Astros have a league best 22.8 percent K-BB%. The Royals’ bullpen has outproduced the Astros’ bullpen, but there are signs indicating that Houston’s pen is actually better.

Who are they?

The bullpen is comprised of a handful of free agents brought in during the offseason and a few returnees. Notably, the players returning to the bullpen were on the squad that had the worst ERA among all bullpens in 2014. The 4.80 mark was a tick behind the lowly Rockies. Even more notably, the bullpen’s 126 ERA- was a full 14 points worse than the second worst.

Chad Qualls, Tony Sipp, Josh Fields, and Samuel Deduno (who has also started a couple of games and is currently on the disabled list) are the returning members of the bullpen. They’ve combined for 57 innings of relief, a 2.05 ERA, and a 52 ERA-. Deduno has performed the worst so far this season. His relief ERA stands at 3.65. But, as noted, he’s currently on the disabled list and in any case isn’t going to receive many high leverage innings. The second-worst ERA among this group is Qualls’s 2.60 mark, but he’s struck out almost thirty percent of the batters he’s faced.

Four new faces complement the four returning. This offseason, the Astros added Luke Gregerson, Pat Neshek, Joe Thatcher, and Will Harris. While their raw numbers aren’t as impressive as the other four on the surface, the newly added arms are the ones getting the most high-leverage work--this group's 2.83 Win Probability Added far outpaces the previous one’s 0.03. This group has combined for 68.2 innings pitched with a collective 2.36 ERA and a 60 ERA-.

The Astros invested heavily in two of these players, Gregerson and Neshek. So far, it’s paying off a bit more with Neshek than Gregerson. In fact, Gregerson has been the team’s worst reliever. He has a committee-high 4.12 ERA and 105 ERA-. Gregerson also strikes out the least amount of batters this side of Deduno. But he also has 12 saves and has blown just one. Gregerson’s situation in the Astros’ bullpen might represent a case in which confining the veteran closer to the ninth inning allows flexibility and optimization prior to it. He’s walking a bit of a tightrope, but as long as his colleagues in relief continue to shut down innings prior to the ninth and he doesn’t start blowing saves, his role appears safe.

Will they stay this good?

The reliable answer: who knows? Bullpens are a collection of a bunch of small sample sizes. The sample is small now, and it will be at the end of the season. Current and historical contextualization of the Astros’ bullpen, however, points us to areas of possible regression. Still, there are reasons to believe that the bullpen can maintain its current excellence.

If the season ended today (it doesn’t), the squad’s ERA and ERA- would rank as the second best bullpen season since 1980. Interestingly, the team ahead of them would be the 2015 Royals and the team behind them in third place the 2015 Cardinals. The run environment and, probably, the time of the season are propping up the figures a bit. But they aren’t too far off being one of the best squads since the advent of the modern bullpen. Fourteen bullpens since 1980 (discounting the shortened 1994 and 1995 seasons) have posted an ERA- between 60 and 69, so the Astros’ current 54 ERA- isn’t beyond the pale of attainability. The Royals' current mark of 40 might be though.

The Astros’ bullpen has a LOB% of 81.4 percent, which is third highest in baseball, and the BABIP against is .239. The highness of the former figure and the lowness of the latter suggest that some regression is coming. Only five bullpens since 1980 have posted a LOB% over 80 percent; however, four of those have come in the last three years, and there are four bullpens that have a LOB% over 80 percent right now. The 2015 Astros are excelling in an extreme environment. The historic figures should be taken with a grain of salt because committees from the past few years populate the top of these leaderboards. But they are still besting their peers.

This is what the bullpen’s effectiveness looks like on a micro level. This past weekend, the Astros traveled to Detroit for a four game set. They lost the first two but took the second two to earn a split. In the two wins, the Astros’ bullpen pitched seven innings, during which they allowed five hits and just one run. Qualls, Thatcher, Fields, Gregerson, Harris, and Neshek combined for these winning efforts.

In terms of results, ERA and ERA-, the Astros bullpen continues to sit well behind the Royals, who lead the league with marks of 1.68 and 42. But in terms of strikeouts and walks, the Astros bullpen has shown signs that it might end up being better. Run estimators believe that to be the case. While both squads are probably due for some regression, they both stand a fair chance at being among the ten best bullpens since 1980. While that might be due to the current run environment and composition of bullpens league wide, they are still quite a bit better than their peers. And that’s what matters in a playoff race. If the Astros do break into the postseason, and they have put themselves into a great position to do so, don’t ignore the bullpen when asking how they did it.

★★★

Eric Garcia McKinley is a contributor to Beyond the Box Score. He writes about the Rockies for Purple Row, where he is also an editor. You can follow him on Twitter @garcia_mckinley.