The NFL has about 1700 or so players. One would figure a few are same-sex attracted. The 10% figure from Kinsey is from a biased sample, but even with a 1% figure, we're looking at one gay guy on every other team, given a 53 man roster.
So, I don't see Michael Sam's outing himself being a huge issue. He's poised to be the first outed NFL (assuming he catches on, which he should) player, but he'll get a better welcome than people think. A lot-of anti-gay locker room banter is often generic insults to the other guy's toughness rather than actual animus towards gays.
Liberals will be supportive and conservatives will be polite; hip-hop culture has a anti-guy streak to it, but even that might be generic trash talk, with rap aficionados being polite to actual gays while hearing them dissed on their Beats.
Likewise, Jason Collins' belated start as an outed NBA player is an interesting milestone. Brooklyn signed him to a 10-day contract, a fill in for a Nets team with few healthy bigs. After all the press his auto-outing saw last summer, the actual first game was an anti-climax, especially when it was a journeyman center who broke the barrier.
For better or worse, we're rather used to gays in the public square now. We may not think they're making good moral choices, but they're in the mix.
I recall a old chant of gay protestors of a couple decades ago-"We're here, we're queer, get used to it!" After a third of century of being thumped with that meme, American culture is just about used to it.