Serena Williams poses with the Daphne Akhurst Trophy after winning...

Serena Williams poses with the Daphne Akhurst Trophy after winning the Australian Open on Jan. 28, 2017. Credit: Getty Images / Scott Barbour

Why does a woman have to beat a man in order to be considered the best player in her sport?

When rating the greatness of a woman athlete, why do we feel compelled to pull her out of her arena of competition and see how she would fare against men? Why isn’t it enough to look at exceptional performances and wins?

This is all I could think of after listening to John McEnroe’s interview with Lulu Garcia-Navarro on NPR on Sunday. In an interview in which he was promoting his new memoir, “But Seriously,” McEnroe called Williams the greatest woman to play tennis but then qualified her greatness by adding that if she played on the men’s circuit, she would be ranked “like No. 700 in the world.”

“That doesn’t mean I don’t think Serena is an incredible player. I do, but the reality of what would happen on a given day is Serena could beat some players, I believe, because she is so incredibly strong mentally,” McEnroe said. “But if she had to just play the circuit — the men’s circuit — that would be an entirely different story.”

There long has been an obsession with seeing how great female athletes compare to men, the most notable being the “Battle of the Sexes” in 1973, when Billie Jean King, in her prime, beat 53-year-old Bobby Riggs in straight sets. You would think we would have made some advancements since then, but the subject of how a woman would fare against men seems to come up again and again.

“The broad issue is why can’t great female athletes simply be great without the constant comparison to men?” said Mary Jo Kane, the director of the Tucker Center for Research on Girls and Women in Sport at the University of Minnesota. “When North Carolina wins the NCAA Tournament, people don’t demand they go beat Cleveland or the Golden State Warriors. In boxing, you don’t ask the middleweight champion to beat the heavyweight.

“The point is lesser — and I’m using the word lesser in quotes — male athletes or teams never get compared in ways that denigrate and marginalize their accomplishments by comparing them to a superior entity. When we do that to women, it takes away from their greatness. They aren’t allowed to be great on their own.”

In other words, if this is the metric we use, then a woman can never be the best. Sadly, that may be the point of some who use it. I don’t think that’s McEnroe’s point. McEnroe, who last won a major championship in 1984, is a feminist when it comes to advocating for equal pay for women and men in tennis. But he does have a book to sell, and he has managed to remain in the public eye because his mouth is still as agile as ever.

McEnroe has been trying to coax Williams into a match for years. President Trump approached McEnroe 17 years ago about playing a $1-million, winner-take-all match against Williams or sister Venus. McEnroe told Jimmy Kimmel two years ago that he believed he still could beat Williams.

Williams, who is seven months pregnant, is busy doing other things. Last week, she was announced as the new ambassador for the Allstate Foundation Purple Purse program, which helps victims of domestic abuse. Monday night, Serena responded to him on Twitter and said, “Dear John, I adore and respect you but please please keep me out of your statements that are not factually based. I’ve never played anyone ranked “there” nor do I have time. Respect me and my privacy as I’m trying to have a baby. Good day sir.”

So you can bet she isn’t going to play McEnroe, or any other man, any time soon. It’s ridiculous to even want her to.