Women's Sports Foundation marks milestone but more work needed, says Billie Jean King

Living legend Billie Jean King said her work is far from over as she celebrates a half century of advocacy for generations of female athletes this week with the 50th anniversary of the Women's Sports Foundation.

The organisation founded by King turned a $5,000 investment into more than $100 million to lift up women's and girls' sports, launching a year after King was catapulted into feminist immortality with her 'Battle of the Sexes' triumph over Bobby Riggs.

"When you're reading history it goes really fast. But when you're living it, it is really, really slow. It's hard," King, 80, told Reuters. "There's going to be a lot of patience and persistence and passion to do what you want to do. If you don't have that, you're not going to last."

"You have to have that 24-hour passion to do what you love, no matter what the outcome." The 12-times Grand Slam winner became the first individual female athlete to receive the Congressional Gold Medal last month in recognition of her unyielding advocacy for equal pay in tennis.

Her protests led to the US Open becoming the first major to offer equal prize money for men and women in 1973 and her Women's Sports Foundation has invested more than $100 million into sports programmes, research and advocacy. While she has witnessed radical change in women's sports since, King says there is still work to be done, citing low numbers of female coaches at the highest level of sport as a key area for improvement for women.

"Nothing would be more wonderful than never needing the foundation, but we do need it desperately," said King, who will mark the 50-year anniversary with a Women's Sports Foundation gala in New York on Wednesday.

"But at the end of the day, the thing that is deemed most important is social justice and rights and freedom."