Impact of Astros Defense on Pitchers’ Performance

When sports broadcasters talk about why the Astros are leading the AL West, they usually just mention the offense. But it’s much less often that defense is discussed. And that’s too bad, because defense is an important reason for the Astros’ performance this year.

The Fielding Bible tabulates a defensive runs saved team leaderboard. The Astros are No. 1 with 55 runs saved above average. The impact of the exceptional fielding performance shows up in the pitchers’ stats. Team fielding and pitching performance, in combination, comprise run prevention.

Fielding Independent Pitching (FIP) does not include the effect of fieldng, but instead focuses on what the pitcher, alone, controls. If a pitcher’s FIP is higher than ERA, sometimes analysts conclude that the pitchers is due for regression. But this assumes that the difference is due to luck. In fact, the quality of the defense behind the pitcher may have a lot to say about whether the ERA is above or below the FIP.

The Astros not only have an ERA (3.64) below its FIP (4.09), but also have the second largest gap between ERA and a higher FIP in the majors (E-F=-0.46). Only the Dodgers have a larger negative E-F. Does this mean that the Astros pitching ERA will regress toward the FIP? The Astros defense says “no.”

If the 55 defensive runs saved are added to the Astros’ earned runs allowed, the Astros’ ERA would be 4.09, which is the team FIP. And this surprises me—I didn’t expect it to be this neat and precise--but the team’s E-F would be zero. Collectively, the Astros’ pitchers are not due for regression to the FIP.

OAA Behind Astros’ Pitchers

The fielding run prevention is not evenly distributed among Astros’ pitchers. For individual pitchers, some element of luck is involved. The only defensive metric which can be filtered to show the fielding results playing behind each pitcher is Statcast’s Outs Above Average (OAA).

I looked at the OAA behind Astros’ starters and several relievers. (I excluded relievers acquired at the deadline, since most of the OAA will be based on other teams’ defense.) I also calculated OAA per hundred fielding plays behind the pitcher. They are ordered by OAA per hundred plays. E-F is also shown; a negative value means ERA is below FIP, and vice versa for a positive value.

(OAA, OAA per 100, E-F)

1. Javier 6/ 4/ -1.37
2. Urquidy 7/ 4/ -0.65
3. Raley 2/ 3.9/ 2.56
4. Valdez 13 /2.7/ -0.81
5. Abreu 2/ 2.6/ 0.17
6. Greinke 4/ 1.07/ -0.93
7. L. Garcia 2 /0.86/ -0.1
8. McCullers 2 /0.79/ -0.27
9. Odorizzi 1 /0.56/ -0.27
10. Stanek 0/ 0/ -0.5
11. Pressly -1/ -1/ -0.19
12. Taylor -2 /-2.66/ 0.17

Photo by John McCoy/Getty Images

The pitchers’ E-F is moderately correlated with OAA (corr.= -0.30). Yet the magnitude of the correlation does not indicate that the fielding will explain each pitcher’s difference between ERA and FIP. Most likely some pitchers were just plain more or less luckier than others. I also suspect that the relief pitchers’ numbers are less reliable due to the smaller sample size. Javier, Urquidy, Raley, and Valdez seemed to benefit the most from good defensive plays, as measured by OAA. Except for Raley, they enjoy an ERA below FIP.

I took a closer look at Cristian Javier, given his high E-F (-1.37) and high level of defense behind him. Without the above average defense, Javier’s ERA would be 3.39 instead of 2.85, which would reduce the gap between FIP and ERA by about 40%.

All of the starting pitchers received at least some benefit from the Astros’ defense. Jake Odorizzi, however, received the least benefit with only 1 out above average. Three relievers did not benefit from the Astros’ defense. Stanek had league average defense behind him (0 OAA), and Pressly and Taylor had below average defensive plays behind them.