It's the biggest move of his career and it's off the court.
Jason Collins, who played with the NBA's Boston Celtics and Washington Wizards this season, has disclosed that he is gay, making him the first active openly gay male athlete in the four major American pro team sports.
The center, who said he is now a free agent, made the disclosure in a column appearing in the upcoming issue of Sports Illustrated.
"I didn't set out to be the first openly gay athlete playing in a major American team sport. But since I am, I'm happy to start the conversation. I wish I wasn't the kid in the classroom raising his hand and saying, 'I'm different.' If I had my way, someone else would have already done this. Nobody has, which is why I'm raising my hand," he wrote.
Collins also wrote that the killing of three people at the Boston Marathon persuaded him to make an announcement. Things can change in a moment, so why not start living more truthfully, he wrote.
On Twitter, Collins thanked everyone who sent him messages of support.
"All the support I have received today is truly inspirational. I knew that I was choosing the road less traveled but I'm not walking it alone," he wrote.
Sports Illustrated's managing editor said Collins was reticent about being a flag bearer.
"It is a much simpler, more personal reason. He wants to have a family," Chris Stone told CNN. "He wants the same life that his twin brother, Jarron, has. This is a secret he's kept for a very long time. He didn't even inform his brother that he was gay until late last summer. ... So much for twin telepathy."
Jarron, who played in the NBA for 10 seasons and was Jason's teammate at Stanford, tweeted to his brother: "Very proud of you."
"Jason Collins has forever changed the face of sports," said the Human Rights Campaign, a civil rights group fighting for gay rights.
It likened the announcement to Jackie Robinson, the first African-American to play in major league baseball in the modern era.
"At a time when millions are reflecting on the life and legacy of Jackie Robinson, Jason Collins is a hero for our own times," the group said.
Former NBA player Charles Barkley, now an analyst for "Inside the NBA" on TNT, told CNN on Monday night that active players shouldn't be surprised that a teammate is gay.
"I think anybody who thinks they never played with a gay player is an idiot," he said on "AC360." "I played with several gay players. It's their own business, and I think they should get to be who they want to be."
Collins is a 7-footer who has played with six NBA teams -- the Wizards, Celtics, Atlanta Hawks, Minnesota Timberwolves, Memphis Grizzlies and New Jersey Nets -- over the past 12 seasons. He has averaged 3.6 points and 3.8 rebounds in 713 career games, and he has had a great deal of playoff experience with the Nets (who have since moved to Brooklyn) and the Hawks.
Momentum had been growing in recent months for an active player in the National Football League, National Hockey League, National Basketball Association or Major League Baseball to come out.
Just a few weeks ago, the NHL announced a new program teaching tolerance and giving support to gay athletes.
Commissioner Gary Bettman said the agreement made the NHL's policy of inclusiveness "clear and unequivocal."
"While we believe that our actions in the past have shown our support for the LGBT community, we are delighted to reaffirm through this joint venture with the NHL Players' Association that the official policy of the NHL is one of inclusion on the ice, in our locker rooms and in the stands," Bettman said in the joint statement with You Can Play.
And NFL player Brendon Ayanbadejo, The New York Times reported, has been in contact with closeted players in several sports.
"What we're trying to facilitate is to get them together and do what they want to do, do what is right for them," he told the Times.
In February, former professional soccer player Robbie Rogers announced on his blog that he is gay. His former U.S. teammates showed solidarity in response to the news.
Though reaction to Collins' announcement also was overwhelming support, not everyone had a positive response.
ESPN basketball analyst Chris Broussard said the Bible calls homosexuality a sin.