When Astros rookie Lance McCullers made his Major League debut on May 18, it took him all of two pitches to do something no other Houston starter has done all season long, before or since: throw a pitch harder than 94 mph. More than 14,000 pitches across baseball have come to the plate that fast so far this season; eight pitchers have done it more than 300 times by themselves. Other than a few particularly hard heaters from reliever Josh Fields, no Astro -- and certainly no one in the rotation -- had crossed the threshold.

In a sport that's always trying to find the next flame-throwing big thing -- average fastball velocity has increased slightly each year since 2008 -- the Astros have taken a completely different approach. They throw their fastballs softer than any team in baseball, with a Statcast™ perceived velocity of just 90.12 mph through Memorial Day. You might assume it's a just a lack of talent on a team coming off six consecutive losing seasons. However, it might actually be a concerted effort to look for something a little different than the traditional big heat -- and it's working.

The 2015 Astros are a little better on offense and a little better on defense, and those both partially help to explain how last year's 92-loss team turned into this year's club with the best record in the American League. But the major change here is in how last year's mediocre pitching staff, which finished 25th in ERA, is this year's surprisingly effective seventh-rated collection.

Houston's pitchers don't throw hard, but they also don't throw it straight. No team in baseball has thrown fewer four-seam fastballs, with only 23.1 percent of their pitches falling under that category. (By comparison, the leader, Tampa Bay, is at nearly 48 percent.) That makes sense; after all, a straight fastball without elite velocity tends to end up in the stands.

Instead, the Astros throw sinking fastballs more than anyone else, sliders more than all but two other teams, and baseball's seventh-highest rate of curveballs. Rather than attempt to blow the ball past the opposition, they attempt to fool them, and that's led to a staff that's managed to limit hard contact on the ball like few others.

Average batted-ball velocity, team pitching

86.97 mph -- Dodgers

86.97 mph -- White Sox

87.26 mph -- Astros

Though the Astros don't put up elite strikeout numbers, they survive by inducing grounders (second-highest ground-ball percentage in baseball) and avoiding walks (fourth-lowest walk rate). Take, for example, their two best starters, Dallas Keuchel and Collin McHugh, and realize the kind of weak contact they're getting:

Average batted-ball velocity, pitcher (min. 50 PA)

84.47 mph -- Chris Sale

84.53 mph -- Clayton Kershaw

84.99 mph -- Wei-Yin Chen

85.18 mph -- McHugh

85.25 mph -- Keuchel

We're still learning exactly how Statcast™ batted-ball velocity holds up over a full season, and how it will correlate to success. But any list that is topped by two of the unquestionably elite starters in baseball certainly passes the sniff test, doesn't it? After nearly 500 combined innings of above-average performance by an unheralded 2009 seventh-rounder (Keuchel) and a Mets/Rockies castoff (McHugh), it's not unreasonable to see the two Astros there, either.

Of the 12 Houston pitchers who have had at least 20 balls tracked, nine of them have a batted-ball velocity at or below the Major League average. Combined, the 2015 Astros staff is making about the same as the $32.5 million that Kershaw is taking home by himself. Other than McCullers, a 2012 first-rounder, this is a group mainly collected via waivers, minor trades or relatively quiet free-agent moves. It's a group that sure looks like it was assembled largely to limit solid contact -- it's sure not about name value.

That's not an accident, really. Pitchers who don't throw hard rarely find huge paydays. As we learn more about Statcast™, pitchers who can make sure the opposition doesn't hit it hard may have something extra to bring to the table come contract time.