CLEVELAND — They held a Home Run Derby at Progressive Field on Monday night, the most extraneous one in the history of this annual, made-for-TV, night-before-the-All-Star-Game exhibition. A sellout crowd packed the stadium, and millions watched the telecast, hoping to see something extraordinary. But as one baseball after another sailed into the skies above Lake Erie, anyone who had paid attention to the first half of the 2019 season was asking this:

How, exactly, was this different from what we’ve been watching on a nightly basis all year?

In 2019, home runs are not a sideshow or an appetizer to the main course. They are the main course. With all due respect to the Los Angeles Dodgers’ blistering pace, the New York Yankees’ injury-riddled rise, the dearth of quality relief pitching, Mike Trout’s continued greatness and Bryce Harper’s strikeout binge, the dominant story line of baseball’s first half — by far — is the unprecedented rate at which baseballs are leaving the stadium.

With 3,691 home runs hit in the first half of 2019, the game is on pace to see its single-season record shattered — by a lot. The current pace of 1.37 homers per team game translates to 6,668 over a full season — 563 more than in 2017, when a record 6,105 were hit. That’s like taking the most homers ever witnessed in one season and adding almost eight 2001 Barry Bondses to it.

“There’s obviously something going on,” Los Angeles Dodgers left-hander Clayton Kershaw, who has contributed 13 gopher balls to this year’s major league total, said Monday on the eve of the All-Star Game. “I don’t know if it’s a good or a bad thing, but they’re flying out of there — I can tell you from experience.”

Even the raw accounting of leaguewide totals doesn’t do justice to the astounding rate of long balls across the game. But maybe this will: Only six teams have ever hit 250 or more homers in a single season, led by the Yankees with 267 last year. But this year, no fewer than 10 teams are on pace to reach or surpass the 250 milestone, and the Minnesota Twins are on pace to hit a staggering 302.

“At our stadium, guys are hitting them almost out of the stadium,” Texas Rangers lefty Mike Minor said. “The ball is just flying. Every series it seems like someone hits one where you’re like, ‘Huh?’ ”

Home runs, with their massive gravitational pull, are like baseball’s equivalent of a black hole, pulling in and vaporizing everything else in its force field, leaving behind a grotesque, distorted version of the game. Home runs have accounted for 15.9 percent of all base hits this season, up from 11.6 percent a decade ago and 8.5 percent 30 years ago.

“The milestone marks, the historic records that seem to be so celebrated across our game — you just wonder if those get tainted as guys chase down some of those records,” Max Scherzer, the ­Washington Nationals’ ace, said Monday.

While fans oohed and aahed over the titanic moon shots off the bats of the derby participants Monday night, they could have just attended virtually any major league game this season to witness the same spectacle. In 2018, there were 82 home runs estimated at 450 feet or more, per Statcast tracking data. This year, there have already been 100. Flyballs are turning into homers at a rate of 15.1 percent in 2019, up from 9.4 percent at the beginning of this decade.

“If the balls are flying 25 feet further this year, I’m glad they’re not just doing that when I’m pitching,” Chicago White Sox ace Lucas Giolito said. “It’s that way for everybody.”

It is when you begin asking the critical question — Why is this happening? — that everyone seems to get a little squirrelly.

“Guys are throwing harder and with more spin,” Dodgers right-hander Walker Buehler said. “When you spin a ball more, it’s going to travel farther when it gets hit.”

“They’re putting guys in the big leagues now who can hit home runs,” Houston Astros third baseman Alex Bregman said. “In the past, the seven, eight and nine hitters would put the ball in play, go line to line and just get hits. And now, one through nine has the power to leave the yard.”

“Guys are throwing more fastballs up in the zone now, [as a counter to] the launch-angle movement or whatever,” Detroit Tigers closer Shane Greene said. “More [batters] have holes up in the zone, and with analytics you can pinpoint that hole. But if you miss your spot up there, it’s going to get hit out of the park.”

“A lot of guys are throwing a lot harder,” said Trout, the Los Angeles Angels’ two-time MVP. “When I first came up [most pitchers were throwing] 90 to 93 [mph], and there was maybe that one guy in the bullpen who could throw 100. Now there’s multiple guys.”

But by this point, there is little doubt that a change in the aerodynamic properties of the baseball is driving the home run surge. Even if the visual evidence isn’t overwhelming, many pitchers have reported a different feel to the 2019 baseball, Commissioner Rob Manfred has acknowledged a reduction to the ball’s drag coefficient, and a Harvard-educated former astrophysicist has proved more or less definitively that the ball’s physical properties have changed this year.

In a piece for the Athletic, Meredith Wills concluded the ball’s seams are “demonstrably lower” this year, creating a rounder, more aerodynamic ball with less drag.

“Our scientists . . . have told us that this year the baseball has a little less drag,” Manfred told ESPN Radio on Monday. “It doesn’t need to change very much in order to produce meaningful change in terms of the way the game is played on the field. We are trying to understand exactly why that happened and build out a manufacturing process that gives us a little more control. [But] our baseball is a handmade product, and there is going to be variation year to year.”

Chicago Cubs Manager Joe Maddon, after witnessing baseballs ricocheting off bats as if they were golf balls, told reporters Sunday, “You could have just stamped ‘Titleist’ on the sides of these things.”

Astros ace Justin Verlander, an outspoken voice about so-called “juiced” balls since 2017, has again led the charge in 2019. Verlander, who will start Tuesday’s All-Star Game for the American League, told ESPN on Monday: “Major League Baseball’s turning this game into a joke. . . . We all know what happened. Manfred [said], ‘We want more offense.’ All of a sudden, the balls are juiced? It’s not coincidence. We’re not idiots.”

But whatever alteration is ultimately made to restore some equilibrium to the game, via the baseball itself, it is unlikely to happen before the end of 2019. Which leaves the question of just how crazy this season is going to get. This May, batters hit 1,135 homers, the most ever for a month in the sport’s history — a record that lasted only a month, when hitters bashed 1,142 in June. And the warmer months of July and August, when home run rates traditionally soar, are still to come.

As Pittsburgh Pirates closer Felipe Vazquez put it Monday: “It’s crazy, man. But you can’t do anything about it, except get out of the way when it’s coming at you.”

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