Astros’ Starting Pitchers Excel Since June 1

The Houston Astros’ starting rotation has made almost a miraculous turnaround this season. The starting pitchers’ performance has gone from extremely disappointing early in the season to among the league’s best over the last two months. What makes this improvement so surprising is that the rotation had to overcome an unprecedented number of injuries at the same time.

I have compared starting pitcher results before and after June 1, which constitute approximately equal samples of the season so far. Before June 1, the Astros’ rotation was ranked 26th in ERA. After June 1, the Astros’ rotation is ranked 3d in ERA, behind only the Mariners and Cubs.

Below are the Astros’ results and ranking for ERA, the advanced metric SIERA, Win Probability Added, and K%:

Pre-June 1: ERA 4.77 (26 Rk), SIERA 4.53 (27 Rk), K rate 21.8% (17 Rk), WPA -0.51 (22 Rk).

After June 1: ERA 3.61 (3 Rk), SIERA 3.80 (8 Rk), K rate 25.4% (2 Rk), WPA 4.41 (2 Rk).

That is fairly dramatic improvement in run prevention during the two halves played so far.

The Astros have the No. 1 ranked Stuff+ since June 1. Notable improvements in pitch type Stuff+ ranking (before/after June 1): 4 seam Fastball from 12th to 4th; Sinker from 7th to 1st; Curve Ball from 8th to 2d.

Spencer Arrighetti was a significant contributor to improvement in Stuff+ from 80 before June 1 to 102 after June 1.

Hunter Brown and Framber Valdez made big improvements in run prevention for pre- and post- June 1 time periods. Since June 1, Hunter Brown is 6th ranked in ERA with 2.35. And over the same time frame, Framber Valdez is 12th ranked in ERA with 2.91.

By contrast, in the pre-June 1 period, Hunter Brown’s ERA was 6.90 and Framber Valdez’s ERA was 4.34.

The Astros have the following starters on the Injured List (IL) currently: Garcia, McCullers, France, Verlander, Javier, and Urquidy. Despite the injuries in the rotation, the Astros managed to turn around the rotation’s pitching results.

The rotation pitching depth remains an issue, given the potential need to monitor the work load of Ronel Blanco, Spencer Arrighetti, and Hunter Brown. Justin Verlander hopefully will return to the rotation by the end of the month, which would permit consideration of a 6 man rotation. It remains to be seen if Luis Garcia, Jr. will be able to return in time to affect the regular season rotation.

Kusei Kikuchi was a mid-season trade acquisition, and so far he has been quite successful in bolstering the rotation. In his two starts for the Astros so far, Kikuchi has posted a 3.27 ERA and 2.82 SIERA with a 15.55 K/9.

Playoff Odds

By winning the Rangers series, the Astros Fangraphs Playoff Odds improved to 61%. The Astros’ PECOTA PLayoff Odds stand at 73%. As we proceed through the final two months of the season, expect the playoff odds to significantly move up and down based on periodic wins and losses. As the “rest of season” becomes smaller, teams’ future wins and losses will pose a greater impact on playoff odds.