Zhang Shuai quits tennis match after opponent rubs out a ball mark with her foot in disputed call

WATCH: Tearful Zhang Shuai Retires Vs. Amarissa Toth After Dodgy Mark Call & Lack of Sportsmanship | Budapest

BUDAPEST, Hungary (AP) — Chinese tennis player Zhang Shuai quit a match after her opponent rubbed out a ball mark with her foot following a disputed line call at the Budapest Grand Prix, with the WTA saying Wednesday that it was investigating an "unfortunate incident."

The second-seeded Zhang retired from the match while trailing 6-5 in the first set against Hungarian opponent Amarissa Toth at the clay-court tournament on Tuesday.

The dispute related to a forehand from Zhang that appeared to be in but was called out. Zhang argued the decision but it stood and the match continued briefly before the disagreement about the line call began again.

As Zhang repeated her protests, Toth walked over to the ball mark and rubbed it out with her foot.

"Wait, wait, wait! Keep the mark," Zhang shouted in response. "What are you doing? Why would you do that?"

Zhang sat crying and shaking her head on her chair for a few moments at the side of the court before quitting.

She shook hands with the main umpire and Toth before appearing to point her fingers at the crowd, which had booed and jeered her for disputing the call.

"The WTA has zero tolerance for racism in any form or context," the WTA tweeted. "The unfortunate incident that took place yesterday at the Hungarian (Budapest) Grand Prix and subsequent posts are being reviewed and will be addressed."

It did not give further details.