Billie Jean King says there's a double standard in tennis when it comes to rules applied to women compared to men.
Serena Williams was penalized a game for calling the chair umpire a thief during an extended argument as the U.S. Open women's final.
Williams clashed with chair umpire Carlos Ramos, demanding an apology after he initially issued a warning for a code violation in the second set's second game for receiving coaching, which is not allowed during Grand Slam matches.
King tweeted, "when a woman is emotional, she's 'hysterical' and she's penalized for it ." King wrote that if a male player had a similar outburst, he'd be called "outspoken" and have no repercussions.
King also tweeted that coaching should be allowed in tennis .