Billie Jean King says that the WTA tour needs more women coaches.

The vast majority of coaches in the WTA are men—e.g. all of the Top 10 women have hired male coaches.

"I think it's still they think guys are better and guys can hit with them," said 70-year-old King, one of the game's greatest players and who has worked on feminism issues through much of her career.

"The best women need people to hit with so they can kind of do two. But today they have everything. They have a hitting coach, a coach coach, whatever you want. I think that's not a good argument anymore. At the top anyway. You don't have as much money at the lower [level]."

Even then, said King, female coaches could be found from among fellow players. "I always think they could use a friend or a player to help coach them if they don't have the money down at the lower ranking," she suggested. "That's fine. We used to help each when we didn't have any money back in the old days and we were the best players in the world. We helped each other.

"I just think it would be helpful if we had more women coaches. Any time you hurt that human capital, only have half of it, you're missing out on a lot. You just are."