We expected the Houston Astros to contend for a playoff spot prior to the start of the regular season, we didn’t expect them to post a 41-30 record while leading the AL West by four games. Houston’s division lead weathered a seven-game losing streak that saw the team’s lead over Texas shrink by five games.

In their last ten games the Astros are 7-3, and they’ve added a 1.5 games to their lead over the Rangers. They’ve earned a 21-14 record against their division, and have posted dominated the National League to-date. Houston has done all of this while posting a +39 run differential — 2nd bet in the American League.

So how, exactly, have the Houston Astros’ been this good in 2015?

The answer lies in the Astros improved pitching and defensive performance, which has been accompanied by the offense hitting for a little more power.

George Springer has been the Astros’ most valuable position player in 2015. (Courtesy of Dobber Sports)

So far in 2015, the Astros’ pitching staff has massively cut down on the number of runs they’ve given up since last season. In 2014, they posted a FIP of 3.93 in 1,438.2 innings pitched; fast forward to 2015 and the pitching staff’s FIP is sitting at 3.63 through 626.1 innings. While the season is still going on, we are well past the point where that number would dramatically swing one way or the other. This means that the pitching staff has drastically reduced the number of runs per nine innings it is responsible for, in just one season.

The bullpen’s improvement from last season to this season has been the biggest reason for the pitching staff’s improvement. Houston’s relievers, as a unit, have sliced their ERA from 4.80 to 2.59 while stranding more runners; in 2014, the bullpen left 67.7% of runners on base…that number has jumped to 81.5% in 2015. Which has led to the pen giving up fewer runs in general, the team’s xFIP (FIP minus home runs) has decreased from 3.90 to 3.01. This improved performance has given the team a greater chance of holding onto late leads, which has led to more wins.

Houston’s pitching staff has also benefited from improved defensive play from the outfield, thanks to the team’s off-season activity. Last year the Astros posted a UZR of -63.9, and a UZR/150 of -12.3, while their outfield defense looked absolutely awful at times…and bad for the rest of it. This season has been a much different story for Houston however, as they’ve posed a UZR of -7.1 in 71 games…and the eye test says that their outfield is reading the ball better and therefore running better routes.

The improved pitching and defense has taken a lot of pressure of the offense because Houston is able to prevent runs from scoring now, and it isn’t up to the offense to win games. Despite the lack of pressure on the offense, Houston has increased its strikeout from 23.8% to 25.2% while walking at a similar rate. In fact, the only thing the offense has improved is its power as team’s slugging percentage has gone from .383 to .426 and the wOBA has increased from .308 to .320.

Despite the increase in strikeouts while increased power output, the Astros have seen massive — and probably sustainable — improvements in their pitching and defense. That’s why the Astros have seen a massive improvement from 2014 to 2015, and are currently leading the AL West by 3.5 games.

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