Jen Welter has become the first female coach in the NFL after being appointed by the Arizona Cardinals.
The 37-year-old American has been hired as a linebacker coach for pre-season by Cardinals head coach Bruce Arians.
He said it didn't matter if a coach was "the Green Hornet" as long as players felt he or she could help them improve.
Welter, who spent 14 seasons as a professional American football player, added: "I'm honoured to be a part of this amazing team."
Arians said he had spoken to his squad about Welter and insisted "they were all very cool" with her appointment.
He added: "I thought she was the type of person that could handle this in a very positive way for women and open that door.
"It's not going to be a distraction in any way."
Welter, who has a master's degree in sports psychology, became the first female to play in a non-kicking position in a men's professional league.
She was a running back and special teams player for Indoor Football League team Texas Revolution in February 2014.
Welter also played as a linebacker for 14 seasons with the Dallas Diamonds in the Women's Football Alliance.
She was also the first woman to coach in a men's professional league after training the Revolution last season.
Welter's appointment is another significant moment for women's sport and US professional sports.
Becky Hammon, an assistant coach for the NBA's San Antonio Spurs last season, served as head coach for the team's developmental summer league team and led them to a championship earlier this month.