The Houston Astros are heading to the Championship Series for the first time since 2005. (Maddie Meyer/Getty Images)

The Houston Astros are heading to the Championship Series for the first time since 2005 after a 5-4 comeback victory on the road over the Boston Red Sox on Monday. Josh Reddick, who started his career in Boston, drove in the go-ahead run in the eighth inning, joining Ray Knight (1986 New York Mets) as the only players in baseball history to drive in a postseason series-winning run in the seventh inning or later against a former team, per Elias.

And although Reddick hit the key single off a 99 mph fastball by closer Craig Kimbrel, the Astros have not been able to get consistent solid contact on pitches with high velocity during either the regular season or playoffs, which is why they won’t want to see the New York Yankees beat the Cleveland Indians on Wednesday in the final game of the ALDS.

The Yankees’ average fastball hit a major league leading 94.5 mph during the regular season, and has become faster during the playoffs (95.3 mph). According to MLB’s Statcast data, the slowest fastball from a Yankees’ pitcher during Game 4 was 96 mph, with an average of 98 mph. The Cleveland Indians, meanwhile, throw a fastball with an average velocity of 92.9 mph.

New York’s flamethrowers can be found in the starting rotation and the bullpen. Closer Aroldis Chapman (average 100.1 mph on his fastball, fastest in the majors this season), setup man Dellin Betances (98.5 mph, third-fastest) and starter Luis Severino (97.6 mph, 15th) can all bring the heat, with Chapman throwing  more pitches over 100 mph (202) in 2017 than the rest of MLB’s pitchers combined.

Throwing faster fastballs has an obvious benefit: they are much harder to hit.

Chapman is holding opponents to a .187 average with 53 strikeouts in 155 at-bats ending on his fastball this season. Betances is striking out more than a third of batters faced (39 percent) with his fastball and Severino threw more than half of his fastballs for strikes (39 of 71) during his Game 4 win against Cleveland, holding the Indians to one extra-base hit in 13 at-bats.

Luis Severino vs CLE, Game 4 of 2017 ALDS. Fastballs only. (MLB)

The league as a whole batted .238 with a .375 slugging against fastballs in excess of 96 mph during the 2017 regular season, compared to a .282 AVG and .476 SLG against fastballs 95 mph and slower. The weighted on-base average, which combines all the different aspects of hitting into one metric, weighting each of them in proportion to their actual run value, was also significantly less against higher-end fastballs: .310 vs. .360 this season, which is roughly the difference between facing St. Louis Cardinals pitcher Adam Wainwright and Pittsburgh Pirates’ slugger Andrew McCutchen.

2017 regular season AVG SLG wOBA
96+ mph fastballs 0.238 0.375 0.310
less than 95 mph fastball 0.282 0.476 0.360

The Astros are a good fastball-hitting team — their .340 wOBA against pitches 96 mph or more this year ranked seventh in the majors — but they surprisingly don’t make good contact as often as they do on fastballs of the slower variety. Just 22 of the 1,198 upper-level fastballs they saw during the regular season were hit on the barrel (also known as the “sweet spot”) or labeled as “solid contact,” the fourth-lowest rate among major league teams in 2017.

2017 Houston Astros vs. fastballs in excess of 96 mph (MLB)

And not allowing high-quality hits makes the Astros easier to get out at the plate. Against fastballs of all types, a ball hit on the barrel by one of Houston’s hitters carried a 1.560 wOBA during the regular season. That dropped by more than half on batted balls classified as “solid contact” (.646 wOBA) and lower still on all other types of balls put in play (.297 wOBA). Against a team like Houston that created runs at a rate that was 21 percent higher than the league average after factoring in league and park effects (121 wRC+) — only the Yankees of 1927, 1930 and 1931 were better — any advantage at the plate could be huge in the playoffs.

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