Brandon Wade / AP

NFL prospect Michael Sam announced on Sunday that he was gay. For reasons that should be obvious, most pro athletes have come out either after they've retired or, as with Jason Collins, toward the tail end of their career when their prospects were in doubt.

This is different:

Mr. Sam, a senior who was listed at 6 feet 2 inches and 260 pounds, had a stellar season as Missouri finished 12-2 and won the Cotton Bowl. He was a first-team all-American and was named the Associated Press defensive player of the year in the Southeastern Conference, widely considered the top league in college football. Teammates voted him Missouri’s most valuable player. Now Mr. Sam enters an uncharted area of the sports landscape. He is making his public declaration before he is drafted, to the potential detriment to his professional career. And he is doing so as he prepares to enter a league with an overtly macho culture, where controversies over homophobia have attracted recent attention. As the pace of the gay rights movement has accelerated in recent years, the sports industry has changed relatively little for men, with no publicly gay athletes in the N.F.L., the N.B.A., the N.H.L. or Major League Baseball. Against this backdrop, Mr. Sam could become a symbol for the country’s gay rights movement or a flash point in a football culture war — or both. Mr. Sam, 24, is projected to be chosen in the early rounds of the N.F.L. draft in May, ordinarily a path to a prosperous pro career. He said he decided to come out publicly now because he sensed that rumors were circulating.

Sam, unlike his predecessors, has his professional career in front of him and a great deal of money on the line. And I suspect there's something more. When black soldiers joined the Union Army they were not merely confronting prejudice—they were pushing the boundaries of manhood. And when the Night Witches flew over German lines, they were confronting something more—the boundaries of humanity itself. Groups define themselves by what they are and what they are not: Niggers are never men, ladies are never soldiers, and faggots don't play football. When Michael Sam steps on a football field, he likely will not merely be playing for his career but, in some sense, for his people.

In that sense he will be challenging a deep and discrepant mythology of who is capable of inflicting violence and who isn't. Last week, Jonathan Vilma speculated about how he might feel if a gay teammate saw him naked:

Imagine if he's the guy next to me and, you know, I get dressed, naked, taking a shower, the whole nine, and it just so happens he looks at me. How am I supposed to respond?

What undergirds this logic is a fear of being made into a woman, which is to say a fear of being regarded sexually by someone who is as strong as, or stronger than, you. Implicit to the fear is the gay player's ability to do violence. It exists right alongside a belief that the gay player is a "sissy." ("Grown men should not have female tendencies. Period," Vilma once tweeted.) The logic is kin to the old Confederate belief that Southern slaves were so loyal and cowardly yet they must never be given guns.