SAN DIEGO — With home runs up to a level not seen since the height of the Steroids Era, baseball Commissioner Rob Manfred says he is not worried performance-enhancing drugs are a reason for the increase.

There was an average of nearly 2.32 home runs per game before the All-Star break, up from 1.90 in the first half of last year and the most before the break since 2.56 in 2000.

“The increase in the number of home runs takes place against a very, very different backdrop,” Manfred told the Baseball Writers’ Association of America on Tuesday. “It takes place against the backdrop where Major League Baseball does 22,000 drug tests a year.”

Thirteen players have been suspended this year under the big league drug program, including NL batting champion Dee Gordon of the Miami Marlins, nearly double the seven suspensions issued in all of 2015.

Offense started perking up during the second half of last season, and last year’s home run average ended at 2.02.

“If it was performance-enhancing drugs, you’d be much more likely to see it begin at the beginning of the season, right, with the offseason being a period of temptation,” Manfred said. “So we think it has to do with the way pitchers pitch, the way hitters are being taught to play the game. We’ve seen some unusual developments in terms of what you traditionally thought of as home-run hitters being moved up in the lineup, just to get them more at-bats.”

Toronto manager John Gibbons at times pushed Jose Bautista, Josh Donaldson and Edwin Encarnacion to the top of his batting order.

Manfred rejected the notion baseballs might be juiced and referred to the resignation in 2013 of Nippon Professional Baseball Commissioner Ryozo Kato after a change in the manufacturing of balls for the Japanese leagues.

“There are certain mistakes in life that if you pay attention to what’s going on around you, you are not inclined to make,” Manfred said. “I like my current gig. So I think you can rest assured … the baseball’s the same as it was last year.”