When former NFL running back Dave Kopay came out in the 1970s, he said, he was "an angry, desperate young man. ... I didn't understand the ramifications of what I did."
He had played in the NFL for nine years before retiring in 1972. At the time, other athletes weren't as forthcoming about their sexual orientation.
"If everyone came out in those days, it would change overnight and, of course, that's what's happening [now]," he said.
So could this be the year a man on a major sports team comes out publicly?
Kopay, 68, said he's not holding his breath.
"It's hard to take always being in the spotlight. I can't imagine what Jackie Robinson went through, for example," he said, referring to the way Robinson broke color barriers by joining the Brooklyn Dodgers in 1947.
Max of ESPN Radio said the first man to come out in one of the four major leagues would need "Balls bigger than whatever ball he plays with in the game."
And thick skin.
OutSports co-founder Jim Buzinski said many players "are in their 20s and not secure with themselves." He speculates that if pros could physically withstand the game into their 40s, a gay male athlete might have already come out on one of America's big teams.
Right now, he added, sports remains "the last closet in American society."
Fear is the number one obstacle.
"No matter how many people tell you it's going to be OK you're still afraid," Zeigler said.
In other parts of the world, there are currently only two high-profile male team athletes who are publicly out. One is Gareth Thomas, England's star rugby player, who divulged his sexual orientation in 2009. This year Swedish soccer player Anton Hysen came out as well, currently the only high-level openly gay soccer player in the world.
The first soccer player to come out, England's Justin Fashanu, reportedly wasn't prepared for the backlash that followed his coming out in 1990. He committed suicide eight years later after moving to the United States.
Today's environment, however, is increasingly different.
'This Is Just the Beginning'
Zeigler said after spending the past decade speaking with athletes who have come out he has "not heard a negative coming-out story in men's sports."
"The number of people speaking up for gay equality in sports and the stature of those people, I know for a fact is going to increase over the summer. This is just the beginning."
Andrew Goldstein, 28, a former Major League Lacrosse player who now has a Ph.D. in molecular biology from UCLA, came out when he was playing NCAA lacrosse at Dartmouth.
He was "terrified" at the time, but decided to speak out after having worried for many years that he could never play openly and also be happy.
Although initially shocked, his teammates not only respected his decision, they vowed to protect him.
"Each one came to tell me that if anyone gave me a hard time, they'd have to deal with my teammates; they'd have my back," Goldstein said.
With all of the positive momentum this year, he said, more people might decide to come out, if "all of a sudden people in the closet start to see, 'It's OK for me.'"