Eight Things That Will Decide the Astros–Red Sox ALCS

This matchup features two of the best offenses in baseball, but hitting alone won't settle the series.

The Astros and Red Sox are matching up for the third time in the past five postseasons. The American League Championship Series is a fascinating matchup between the No. 1–ranked offense against No. 4, two scalding-hot teams, two hitter-friendly ballparks and two franchises that were disciplined for misusing in-game technology, though the Houston scandal was far more egregious. Here is a look at some of the most important factors that will decide the series.

Carlos Correa and Xander Bogaerts :: Troy Taormina/USA TODAY Sports; Bob DeChiara/USA TODAY Sports

Bullpen use

I said before this postseason began that you had to lose your traditional sense of what wins in October. It is not starting pitching. It is bullpen use. Starters have become game managers in October. Bullpens decide games. After 18 postseason games entering NLDS Game 5 on Thursday, relief pitchers have thrown more innings, won more games and picked up more decisions than starters. The average start was just 4.1 innings, and only two of the 36 starters reached 100 pitches.

	Record	Innings Pitched
Starters	7–10	153
Relievers	11–8	167 2/3

Lance McCullers Jr.'s forearm

McCullers left his ALDS Game 4 start with tightness in his right forearm. Before any imaging was done, McCullers told me he felt it in his flexor tendon area. He said he was prepared to throw Gavin Sheets an inside fastball to start the fourth inning, but then saw catcher Martín Maldonado put down the sign for a slider. He quickly regripped without getting the best grip on the baseball and felt a twinge upon release. McCullers threw only six fastballs among his 26 pitches that inning.

McCullers is not just Houston’s ace who is throwing the ball well (4–1, 2.17 in his past eight starts) but also a big-game pitcher who has pitched in four postseason clinching wins. In seven potential clinchers he has a 2.96 ERA. If healthy, he would be lined up to pitch a possible Game 7.

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Alex Cora and his rovers

The Boston manager will use starters Nathan Eovaldi, Chris Sale, Eduardo Rodriguez and Nick Pivetta out of the bullpen between starts. His use of the “rover” position was a winning strategy in the 2018 postseason and he will do it again. Houston manager Dusty Baker will deploy a more traditional bullpen.

Any comparison of regular-season bullpen numbers is irrelevant because of the way Cora runs his 'pen in the postseason (and the addition of Hansel Robles) and because of Houston’s trade acquisitions, Phil Maton and Kendall Graveman.

Red Sox fastballs vs. Astros hitters

The Astros were the No. 1 hitting team vs. fastballs this year (.289). The Red Sox ranked tied for fifth (.279). Both teams have been crushing heaters this postseason. Boston pitchers must throw more secondary pitches in this series. You are not beating the Astros with fastballs, as Chicago found out in the ALDS.

Postseason Hitting by Pitch Type

	Fastballs	Secondary
Astros	.375	.137
Red Sox	.330	.325

This will be an especially key matchup when Nathan Eovaldi starts for Boston. Eovaldi has the third-fastest four-seamer among starters (behind Gerrit Cole and Zack Wheeler), but it’s a low-spin heater that gets hit, particularly by right-handed hitters and especially when it is not at the top of the strike zone. Eovaldi likes to throw his fastball to lefties with some up-and-away run, but it is rather straight against righthanders.

Batters hit .312 against his fastball, the fourth-highest among pitchers who threw 1,000 four-seamers.

Rafael Devers vs. fastballs

The Astros this season threw Rafael Devers 105 fastballs out of 113 pitches—an unheard of 93%.

Astros Pitching vs. Rafael Devers, 2021

	Number of Pitches	Avg.
Fastballs	105	.227
Secondary	8	.250

Why would they do that? They follow the numbers. Devers is a great breaking ball hitter. He has the highest slugging percentage against secondary pitches in MLB (.587). He hits .298 against secondary (ranked sixth-best) but only .266 against fastballs (94th).

Devers has been better lately against fastballs. (His problem against heaters is when he overswings his stride gets too long and it causes him to be late.) But Houston will make him prove he can heat fastballs in this series.

Red Sox vs. Framber Valdez's curveball

The Red Sox have seen 69 curveballs from the Houston lefty. They still don’t have a hit against it (0-for-24 with 15 strikeouts).

They’re not alone. Valdez more than doubles his curveball use when he gets to two strikes, when it becomes the sixth-best put-away pitch in baseball (32%). Batters hit .123 against his two-strike curve. Boston is an aggressive-hitting team. It has the sixth-highest swing percentage in MLB. Look for the Sox to be even more aggressive against Valdez to stay away from two-strike counts.

The biggest difference is “D”

Houston is an elite defensive team. Boston is below average. That’s especially a problem against the Astros, who put the ball in play more than any other offense.

	Defensive Efficiency	MLB Rank
Astros	.713	3
Red Sox	.659	30

	Defensive Runs Saved	MLB Rank
Astros	78	3
Red Sox	7	18

Chris Sale’s changeup

It’s gone missing. In his past two games, Chris Sale has thrown only six changeups among his 92 pitches and not recorded an out on the pitch.

Truth is, he has not had the right feel for the pitch since coming back from Tommy John surgery. He is throwing it harder with less sink. Cora said he was encouraged to hear Sale made an adjustment in his last bullpen session and “found something.” The last time he heard that, he said, was when David Price found his changeup with a mechanical fix just before the 2018 ALCS vs. Houston.

Sale Changeup by Month

	Pct.	Velocity	Batting Avg. Allowed
August	22%	86.5 mph	.429
September	22%	86.9 mph	.417
October	7%	86.9 mph	1.000