JABO: Is the Astros Bullpen for Real?

The Houston Astros are 31-20 and on top of the AL West by four games. They’ve been winning in a signature way: by striking out a lot (the most in the league), hitting a lot of home runs (the most in the league), and recording a string of solid starts (10th-highest WAR among starting staffs). One way we didn’t expect the Astros to dominate this season, however: their bullpen. After two months, the Houston bullpen is ranked first among all major-league teams by strikeout and walk rate, and they also have the second-best ERA. Is this just a run of early-season success? Or, like the Royals, have the Astros built a relief corps that only a select few clubs have?

The bullpen was a major focus of the Astros’ offseason plans before the start of the 2015 season, as they added Pat Neshek, Luke Gregerson, Will Harris, and Joe Thatcher to a group that finished dead last in bullpen ERA in 2014. Neshek and Gregerson were brought in as high-pressure help, with Gregerson installed immediately into the closer role. Gregerson has struggled (relatively speaking) to the tune of a 3.74 ERA, but he’s really been the only one in the bullpen who hasn’t been lights out, and he’s chosen great times to be bad, blowing only one save.

What’s been the key to the success for the Astros bullpen? First of all, they’re striking out an incredible rate of opposing batters. Houston relievers have struck out 28.8% of the hitters they’ve faced — a figure which would be the most ever for a bullpen in history. They’ve also limited walks, only handing out free passes to 6.2% of opposition batters. That walk rate would be good for 25th-best in baseball history if the season ended today. Looking at these two figures, it’s not hard to see why the Houston bullpen has been great: success usually follows pitchers who strike out a high percentage of batters while keeping walks to an absolute minimum.

This mostly unexpected domination out of the Astros bullpen has come from a few unlikely places. First, there’s newcomer Will Harris, who’s struck out 29 batters in 24 innings of work while posting an elite ground-ball rate (58.3%). As the most-used pitcher out of the Houston pen, his two pitch, hard cutter/curveball combination has been very effective in two parts of the strike zone: 10 out of his 13 strikeouts with the cutter have been in the upper half of the strike zone and above, while all but one of his 11 strikeouts with his curveball have been in the lower half of the zone and below. This is what success in changing eye levels looks like:

 

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