"Less than three miles from my apartment, nine jurists argued about my happiness and my future. Here was my chance to be heard, and I couldn't say a thing," he writes.
After being a first-round draft pick in 2001, Collins has averaged 3.6 points and 3.8 rebounds for the New Jersey Nets, Memphis Grizzlies, Minnesota Timberwolves, Atlanta Hawks, Celtics and Wizards. He's come to be known more for personal fouls — he led the league in that category one season — than flourish.
"I go against the gay stereotype, which is why I think a lot of players will be shocked: That guy is gay? But I've always been an aggressive player, even in high school. Am I so physical to prove that being gay doesn't make you soft? Who knows? That's something for a psychologist to unravel," he says.
As for what response other NBA players will have to his revelation, Collins writes: "The simple answer is, I have no idea."
"Openness may not completely disarm prejudice, but it's a good place to start. It all comes down to education. I'll sit down with any player who's uneasy about my coming out," he says in his account, adding: "Still, if I'm up against an intolerant player, I'll set a pretty hard pick on him. And then move on."
Former teammate Jerry Stackhouse, now with the Brooklyn Nets, wrote in a text to the AP: "I hope Jason is received well by our NBA family. ... I've already reached out to him personally to show support and will encourage more guys to do the same."
NBA Commissioner David Stern said in a statement: "Jason has been a widely respected player and teammate throughout his career and we are proud he has assumed the leadership mantle on this very important issue."
While Collins is the first male athlete in a major North American professional league to come out while intending to keep playing, several have previously spoken after they retired about being gay, including the NBA's John Amaechi, the NFL's Esera Tuaolo and Major League Baseball's Billy Bean.
"I think he is immensely brave. I think it's a shame in this day and age he has to be immensely brave, but he is," Amaechi told the AP. "He's going to be a remarkable and eloquent spokesperson for what it is to be a decent, authentic human being — never mind just for gay people."
Rick Welts, president and chief operating officer of the NBA's Golden State Warriors, is openly gay.
"He probably knows what he signed up for. There'll be a whole bunch more television reporters and cameras than he's probably had in the past. ... There had been a long bit of speculation about when, who, how. I think that speculation has been put to rest now," Welts said, "and we'll always remember that Jason Collins was the first man to do this."
Collins says that if he remains in the NBA, he could face uncomfortable reactions from spectators.
"I don't mind if they heckle me. I've been booed before. There have been times when I've wanted to boo myself. But a lot of ill feelings can be cured by winning," he writes.
In February, former U.S. soccer national team player Robbie Rogers said he was gay — and retired at the same time. Rogers is just 25, and others have urged him to resume his career.
"I feel a movement coming," he tweeted after word of Collins' news broke.
Some female athletes have found more acceptance in coming out; Brittney Griner, a two-time AP college basketball player of the year and the No. 1 pick in the WNBA draft, caused few ripples when she said this month she is a lesbian. Sheryl Swoopes, a former WNBA All-Star, came out in 2005 during her playing days.
Tennis great Martina Navratilova, who came out decades ago, tweeted Monday that Collins is "a brave man."
"1981 was the year for me — 2013 is the year for you," her post said.
Collins told ABC that Navratilova was his role model.
"I look at her as one of my heroes. ... Hopefully going forward I can be someone else's role model," Collins said.
Sports leagues in Britain and elsewhere in Europe have been trying to combat anti-gay bias. But the taboo remains particularly strong in soccer, where there are no openly gay players in Europe's top leagues and homophobic chants are still heard at some games.
Soccer "is not going to change," said Amaechi, who is English and now lives in Manchester. "If it wanted to change, it would change. It has the resources to do so. It doesn't want to change."
Justin Fashanu is the only significant British soccer player to have come out publicly, doing so in 1990. The former Nottingham Forest and Norwich City striker was found hanged in a London garage in 1998 at age 37. According to an inquest, Fashanu left a note saying that, because he was gay, he feared he wouldn't get a fair trial in the United States on sexual assault charges. Maryland police were seeking him on charges that he sexually assaulted a 17-year-old boy.
Among other athletes outside the U.S. to come out was Gareth Thomas, a Welsh rugby star who attracted widespread media attention in 2009 when he announced he was gay. He continued playing until retirement in 2011.
Orlando Cruz of Puerto Rico came out in October as the first openly gay professional male boxer. Canadian swimmer Mark Tewksbury came out six years after winning a gold medal in the backstroke at the 1992 Barcelona Games. Four-time Olympic diving gold medalist Greg Louganis of the U.S. revealed he was gay in 1994, a year before announcing he was also HIV-positive. Former Olympic skiing gold medalist Anja Paerson of Sweden announced last year, after retiring, that she was in a long-term relationship with a woman.
In SI, Collins recounts that the first relative he came out to was his aunt, Teri Jackson, a San Francisco Superior Court Judge.
"I don't think Jason looked at his life as being a trailblazer," Jackson said Monday. "He has no regrets coming out. And he wants to play. And we'll see what happens next."
Collins says he told his twin brother, Jarron, last summer. Jarron was also a longtime NBA center who last played in the league in the 2010-11 season.
"He was downright astounded," Collins says.
Collins writes self-effacingly about his journeyman NBA career and a parlor game he calls "Three Degrees of Jason Collins," explaining: "If you're in the league, and I haven't been your teammate, I surely have been one of your teammates' teammates. Or one of your teammates' teammates' teammates."
That joking, though, leads to a larger point.
"Some people insist they've never met a gay person. But Three Degrees of Jason Collins dictates that no NBA player can claim that anymore. Pro basketball is a family. And pretty much every family I know has a brother, sister or cousin who's gay," Collins concludes. "In the brotherhood of the NBA, I just happen to be the one who's out."
AP Sports Writers Tim Reynolds, Joseph White, Nancy Armour, Larry Lage, Brian Mahoney, Antonio Gonzalez, Rachel Cohen, Paul Newberry, Jimmy Golen, Howard Ulman, Rob Harris, Stephen Wilson, Richard Rosenblatt and Tom Withers, and Associated Press Writers Mary Clare Jalonick, Cara Rubinsky, Jennifer Agiesta, Steve Peoples, Josh Lederman and Terry Chea contributed to this report.
Howard Fendrich is on Twitter at http://twitter.com/HowardFendrich