Rennae Stubbs has called out toxic behavior by fans at the US Open after a crowd member yelled a Hitler slur in a recent match.

Stubbs, who is an ex-coach of Serena Williams and a former World No. 1 in doubles, has been doing several on-court interviews with players at this year's New York major.

For the most part, the tournament seems to be going well, with fans cheering the players along and showing support for their favorites. However, there have been several instances of fans behaving inappropriately, leading Stubbs to speak out.

Bad behavior began all the way back in qualifiers, when one crowd member started an outraged rant at former player and tennis coach Viktor Troicki. The outburst was so bad that another fan threatened to call the police.

Following this, Stubbs claimed that a drunk woman at Flushing Meadows threw a drink over her during an argument with her boyfriend.

However, nothing was quite as horrible as when a fan decided to yell a Hitler slur during the Round of 16 match between Alexander Zverev and Jannik Sinner. The pair were locked in the middle of the five-set thriller when the situation occurred.

The German player complained to the umpire, telling them that someone in the stands had just said "the most famous Hitler phrase" to him. The crowd member was then removed from the venue.

Stubbs expressed her anger and disappointment on X, formerly known as Twitter, writing:

"There are some fans this late at night @usopen that are not good! I [love] the fans but at this point there are some bad characters. I had a drink thrown on me last night by a drunk fan who was fighting with her boyfriend. Now we got someone yelling Hitler slurs! Wtf? Come on peeps."