Which Staff is Better, the 2018 or 2019 Astros? Willie McGee’s Twin gets the last word.

Editor’s Note: This week Mike Petriello argued that the 2019 Astros staff might be the best in history, better even than the 2018 Astros, because it has the lowest on base percentage recorded in modern times. I countered that in terms of run prevention the 2018 Astros were better, perhaps one of the top five staffs in history. Below our own Willie McGee’s Twin gets the last word.

The goal here is to try to separate pitching from defense.

If one genuinely wants to separate pitching from other factors (team defense, catcher, umpire, batter), then we need to have expected run values per pitch (with and without game-state context would be my preference, including the effects of sequencing and the level of competition!). However, while I think a team like the Astros already has modeled that internally, we don’t have a public version of that.

The best we have now is xwOBA for pitchers.

In 2019, Astros pitchers have an xwOBA of .286, which is the best in baseball by one point over the Rays and three points over the Dodgers.

In 2018, Astros pitchers had an xwOBA of .278. That was the best in baseball by 8 points over the Dodgers.

So, doing our best to exclude the effect of defense, and focusing on BBS, Ks, and quality of contact, Astros pitching was a bit better last year.

How does the team defense stack up? Does a better team defense this year explain how the Astros could be better by other measures, like OBP and BA?

The answer is yes. In 2019, the Astros have the best defensive efficiency in MLB at .737, by a lot! (turning batted balls into outs). https://www.baseball-reference.com/leagues/MLB/2019.shtml

In 2018, the Astros defensive efficiency was worse (.705), and the Astros were 4th in MLB. Thirty-two points of defensive efficiency is a big difference.

What about Statcast? Does it say the same thing?

If we want to measure defense (but not pitching) by Statcast, I think the best measure is xwOBACON – wOBACON.

In 2018, by this measure, the Astros were at -.003. So, basically, the defense gave up a very slightly worse actual wOBACON than the pitchers allowed. The pitchers gave up the lowest xwOBACON in MLB (so we have great pitching and averag-ish defense).

In 2019, by this measure, the Astros are at -.001. So, not very different. But the Astros pitchers are giving up a slightly higher xwOBACON, because they are giving up more HRs. Also, I think this explains some of the reason why we don’t see a difference here between 2018 and 2019 (because the Astros fielders can’t catch balls over the fence).

In sum, the pitching has been awesome both years. 2018 pitching was probably a bit better (including because offense goes up as the season progresses and we’re still early in 2019) but it looks like the Astros 2019 defense is better, so the Astros are doing a better job of turning balls hit in the field of play into outs.

Posted by Willie McGee’s Twin