It isn't, and as a result, a player was penalised for the actions of her coach.
Mouratoglou controversially admitted to coaching Williams from the sideline, saying that it was not an uncommon occurrence in the game.
The tennis superstar sat down with The Sunday Project, an Australian news show, in an interview set to air next weekend - and she's not backing down from her position, despite her own coach now actually admitting otherwise.
'I just don't understand. "We've never had signals".
But for now Osaka is itching to do normal stuff - like catch up with big sister Mari, who is also a professional tennis player, go shopping and eat her favourite matcha ice cream.
"For me, I don't feel sad because I wouldn't even know what I'm expected to feel", she told a news conference in Yokohama ahead of the Pan Pacific tournament that begins on Monday. Ms Williams should have accepted his ruling but, rather than focus on getting back into the match (which she was losing), she let it stew to the point that when she lost the next game she smashed her racquet onto the court - an automatic violation.
During the altercation and again after the match, Williams suggested that sexism was part of the reason why she was punished so severely, although Strycova told Czech website Sport.cz that she doesn't agree.
The incident drew a volley of commentary in recent days.
US Tennis association chief executive Katrina Adams has been overheard apologising to controversial umpire Carlos Ramos just days after she declared chair umpires have "double standards" when dealing with men's and women's matches. A cartoon caricature of Williams appeared in an Australian newspaper drew comparisons to US racial stereotypes of the past.
In Croatia, US Davis Cup team captain Jim Courier said he thought the gender issue had been polarised and, in some ways, politicised. "I'm 36 years old", she said.
O'Hagan praised Williams for calming a riled-up audience that booed the U.S. Open outcome to refocus the moment on Osaka's victory.
"He said he made a motion, I don't understand what he was talking about. That's what it's all about".
"I find it interesting that she did it only when she was losing".