While the Yankees have not always lived up to to their “Bronx Bombers” moniker this season, they did contribute Tuesday night to Major League Baseball’s near-historic home run rate.

Starlin Castro and Chase Headley homered in a 7-1 win over the Orioles, doing their part to boost a leaguewide homer-per-game rate which is the second highest of all time. Big-league teams came into Tuesday averaging 1.15 home runs per game, the most since the record-setting 2000 season (when teams averaged 1.17 home runs).

The Yankees came into the night ranking just 21st in home runs with 96 (1.04 per game), around the majors, balls are leaving yards at rates comparable to the so-called “steroid era,” though it is difficult to pin down why.

“I don’t know if anyone has any better explanation than anyone else,” said Orioles outfielder Mark Trumbo, who leads the majors with 28 home runs. He said some theories include “guys pitching up in the zone more now than they ever had, might be more mistakes.”

Other possible factors, Trumbo said, include warmer weather, pitchers throwing with more velocity, and players swinging the bat more often. “But I think, overall, what might make more sense is that with the shift defense, now more than ever, it’s undesirable to hit the ball on the ground . . . But at the end of the day, there’s no one explanation.”

Carlos Beltran leads the Yankees with 19 home runs and his 5.7 percent rate is his best since 2006, when he hit a long ball in 6.7 percent of his at-bats with the Mets. Beltran attributed his productivity this season to slight adjustments he made last year and keeping his approach consistent, but said he was unsure of what is driving the leaguewide spike.

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He is not alone. In March, FiveThirtyEight.com’s Ben Lindbergh and Rob Arthur wrote a detailed analysis of this power surge that began late last season (which included an inspection of the baseballs themselves), but did not reach any hard conclusions.

Whatever the cause for their increase, home runs partially explain why the Yankees are on the outside looking in relative to the postseason. In addition to not hitting them at even an average rate, the Yankees have allowed the third-most long balls in baseball.

Also, the American League East-leading Orioles are first in the majors in home runs, and the Blue Jays — who lead the Yankees by five games for the second AL wild-card spot — are second.