Rennae Stubbs reveals reason behind Serena Williams' anger towards chair umpire during 2018 US Open final defeat to Naomi Osaka

Former doubles World No. 1 Rennae Stubbs has spoken about Serena Williams' outburst during her defeat to Naomi Osaka in the 2018 US Open final.

Osaka won her maiden Grand Slam singles title at Flushing Meadows but the match is more remembered for Williams' heated argument with chair umpire Carlos Ramos.

Ramos gave the American legend a warning for coaching, though she insisted she was not getting coached. Williams berated the Portuguese several times after that, calling him a liar and a thief.

Ramos subsequently gave her a game penalty for verbal abuse and the situation escalated to the extent that the supervisors had to intervene. The 23-time Grand Slam champion later broke into tears in the intense atmosphere, claiming that she was not being coached during the match.

Rennae Stubbs shared her thoughts on the incident while discussing coaches giving advice during matches on The Rennae Stubbs Tennis Podcast. The Aussie said that the whole situation regarding coaching changed after Serena Williams' controversial moment during the 2018 US Open final.

"Everybody coaches, every player looks to their coaches for advice, and every coach gives it when they can, when the umpire is not looking at them or when the linespeople are not looking at them. It was always a part of the tennis world, always," Stubbs said.

"The situation, it really got changed, let's be honest, when the s*** hit the fan with Serena at the (2018) US Open because a lot of people were like, 'Well he gave a very innocuous signal which was like these two hands together moving forward. What does even that mean?'" she added.

Stubbs, who coached Serena Williams at the 2022 US Open, said that the American legend wasn't even looking at her then-coach Patrick Mouratoglou when he made the gesture that caused the ruckus. The Aussie claimed that Williams wasn't someone who would look at her coaches for advice during a match.

"Second of all, Serena wasn't even looking at him at the time because they showed the split screen, they showed the split screen when he did it and what she was doing, and she wasn't even looking at him. She didn't even look so that's why she got so angry because I can tell you, I know for a fact after coaching her somewhat a little bit now, she doesn't look," Stubbs said.

"I could coach her at the US Open, I actually could tell her a little something and I did a couple of times but she's not the person that looks at you like, 'What do I do?' So that's why she was so pissed," she added.

"I wasn't being coached" - Serena Williams on the 2018 US Open final controversy

Serena Williams during the 2022 US Open

While speaking at her post-match press conference, Serena Williams insisted that Carlos Ramos didn't need to give her a warning as she wasn't being coached.

"No, because I wasn't being coached. If I look at my box and they say, C'mon, or, Good job, I don't know what else to do. After that I didn't even look at my box anymore," Williams said.

Serena Williams reached another US Open final in 2019 but lost to Bianca Andreescu. The 41-year-old wrapped up her illustrious tennis career after a third-round defeat to Ajla Tomljanovic at the New York Major last year.