No other athletes in the four men’s professional sports leagues — the N.F.L., N.B.A., M.L.B. and N.H.L. — are openly bisexual or gay. This is only the second time an active N.F.L. player has openly identified as L.G.B.T.Q.

“Ryan’s Russell’s decision to come out will undoubtedly have a big impact on L.G.B.T.Q. acceptance in professional sports,” Zeke Stokes, chief programs officer for the advocacy group Glaad , said in a statement on Thursday. “Everyone should be able to bring their full, authentic selves to work, and that includes the N.F.L.”

Sarah McBride, the national press secretary for Human Rights Campaign, said, “Ryan Russell is creating more space and opportunity for young L.G.B.T.Q. people to dream big and to pursue their goals.”

The N.F.L. and the N.F.L. Players Association did not immediately respond to requests for comment on Thursday.

In 2014, the N.F.L.’s first openly gay player, Michael Sam, was drafted by the St. Louis Rams — now the Los Angeles Rams — in the seventh round. Sam’s path to the N.F.L. was widely chronicled at the time.

But Sam, an all-American at the University of Missouri and a co-defensive player of the year in the Southeastern Conference in 2013, was cut by the Rams and never played a down in the N.F.L. In 2015, he said he was stepping away from the game for “mental health” reasons after a brief stint in the Canadian Football League.

Russell said one of the people he had reached out to was Ryan O’Callaghan, a former member of the New England Patriots and Kansas City Chiefs who last played football in 2010 and came out as gay two years ago.