“I would not let my son play football,” the president said in a lengthy interview with The New Yorker. “At this point, there’s a little bit of caveat emptor. These guys, they know what they’re doing. They know what they’re buying into. It is no longer a secret. It’s sort of the feeling I have about smokers.”

Mr. Obama recently has made a habit of wading into NFL issues. In an interview with the Associated Press last year, he said the Washington Redskins should consider changing the team’s nickname if Native Americans are offended by it.