In 2014 gay marriage is on the March across America and gays and lesbians are now allowed to serve proudly in the U.S. Military. But tonight one young man is attempting to go where no openly gay man... See More
In 2014 gay marriage is on the March across America and gays and lesbians are now allowed to serve proudly in the U.S. Military. But tonight one young man is attempting to go where no openly gay man has gone before -- an NFL locker room. His name is Michael Sam. He's an all-american defensive lineman with a fascinating back story. And ever since he came out on ESPN's "Outside the lines," reaction has been pouring in from across the league. Not all of it positive. Here's Chris Connelly. Sam taking it in for the mizzou touchdown! This is just telling someone that hey, I'm gay and that's it. It's nothing -- it's not a big deal to me. Right there because that's all it takes. Reporter: It has proven to be a big deal to everyone else. Michael Sam, now the first openly gay NFL draft prospect, out and proud, he says. Speaking with ease about dating another man back at the university of Missouri. I know what I want. I know that I can have a relationship now with a man. We went out publicly. We had dinners together. Movies. Holding hands. Reporter: Will others in the NFL have a problem? The sports world is keen to see how the league's 32 franchises, not all of them known for cutting-edge social awareness, will deal with an S.E.C. Defensive player of the year, a quarterback-sacking force, poised to become the first openly gay player in the history of the league. What kind of reaction do you anticipate getting? You know, there will be negative reactions all around. I expect it. But there are going to be positive. That was Michael Sam! Reporter: There are also uncertainties as the pro football world confronts a new reality. Many sounding unsure about how they think others might react. For me to sit here and say 32 organizations will say no, it doesn't raise a red flag, that wouldn't be the truth. I think some organizations will look at it and ask themselves this question, do we want the drama? Do we want the drama of the media blitz that's going to happen when he ariefsz Rives on our campus? And that's what some teams will wrestle with. Taken down for a loss by Michael Sam. By announcing his sexual orientation before the draft in may, Sam defused a whisper campaign that he feels might have commandeered his story. Why do you think it's important for the NFL to know this about you before the draft? Once scouts came and asked about me, you know, they told about like Michael Sam is gay. And but I didn't know how many media actually knew. And I was afraid it would leak out without me actually owning my truth. I wanted to let the world know and tell them hey, I'm gay, let me tell my own story. Reporter: In fact, as they sought to learn more about the players eligible for the draft this spring, many NFL scouts were already aware that Sam was gay. Agents approached by scouts with questions like what's his girlfriend like? When you spend time with him, are there girls around? There were questions that they didn't get about anybody else. And they realized very quickly that it was the worst-kept secret in football. Reporter: An official statement from the NFL praised Sam for his honesty and courage. Yet some nfl-ers question if locker rooms were ready for an openly gay man. On "Sportscenter" former linebacker Antonio pierce said he'd heard from some current players. To say that they were -- will be comfortable with it was what I got out of them. I wouldn't be really comfortable. You're watching what you have to say and different things of that nature. Remember, this has not been in the locker room in the national football league knowing ever. Reporter: Just before the super bowl in 2013, San Francisco 49ers cornerback Chris Culliver made these comments on the Artie Lange show. I don't do the gay guys, man. I don't do that. Are there any on the 49ers? No. They ain't got no gay people on the team. You know, they got to get up out of there if they do. Can't be with that sweet stuff. Really? Is that true? Yeah, it's true. Culliver later apologized for the comments and said "They are not how I feel." And in a recent interview with the NFL network Jonathan Vilma said this about the prospect of having a gay teammate -- I think that he would not be accepted as -- as much as we think he would be accepted. I don't want people to just naturally assume like oh, we're all homophobic. It's really not the case. I 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? How prepared do you think you are for what that locker room experience will be like? It's a workplace. It's a business workplace. And we have to act professional. And I mean, I know that I am not -- I've never been attracted to my teammates because I don't want that problem. Reporter: If Sam seems unconcerned about the whole thing, it may help to know a little about the obstacles he's already had to overcome. There were some hardships. There was some tragedy and some adversity. Telling the world I'm gay is nothing compared to that. Reporter: Sam grew up in Hitchcock, Texas, a small town outside galveston. And to say he had a tough childhood would be a bold understatement. I endured so much in my past, I -- so much tragedy. And growing up seeing my older brother killed from a gunshot wound. Seeing my -- knowing that my oldest sister died when she was a baby and I never got a chance to meet her. My older -- my second oldest brother went missing in 1998 and me and my little sister was the last ones to see him, and we pronounced him dead two years later. Reporter: In high school Sam says he suspected that he might be gay but says he wasn't certain until he got to college. Last August he came out to his Missouri teammates during a preseason meeting. I used the opportunity just to tell them that I was gay. And their reaction was like Michael Sam finally told us, even though they knew, it was out, it was public, it was news. What was it like to tell your teammates at mizzou? I was kind of scared even though they already knew, but I was still scared of telling them. And just to see their reaction was awesome. Reporter: Mizzou head coach Gary Pinkel discussed that on the "Mike and Mike" radio show. The next morning he came in and, first of all, I gave him a hug and told him I loved him. And you know, you've got our 100% support. And we have to talk about now, you know, what do you want to do? Do you want to come out now? Do you want this to -- after the season? You know, after the NFL draft? Whatever. What are you thinking here, Michael? Reporter: His teammates were free to share Sam's story but did not. It's just something that, you know, you kind of -- just kind of figured it out as you got to know Michael as a person. It's just something that just kind of -- you know, we became comfortable with as a team. And you know, it was no big deal to us. Personally, I'd known for a few years. So it wasn't a big deal to me. I still support Mike. I love him. He's family. But definitely before the draft I thought it was a big deal for him to come out because that could affect his draft stock. Reporter: Some franchises may not think they can handle an openly gay player. Others may worry about Sam's size. He is just 6'2". As he transitions to the NFL. Being picked later in the draft can cost a player millions. All Sam wants, he says, is the opportunity to play the game he loves. Is there a franchise or a city that you might be uncomfortable going to in the draft? No. I just want to go to the team who wants -- who drafts me because I know that team knows about me, knows that I'm gay, and also knows that I work hard and am just an awesome person. That's the team I want to go to. Reporter: For "Nightline" I'm Chris Connelly, ESPN. By the way, Jonathan Vilma
This transcript has been automatically generated and may not be 100% accurate.