Roger Federer said he thinks fellow tennis legend Serena Williams "went too far" in her controversial criticism of the umpire in the 2018 U.S. Open final.

Williams was involved in an angry exchange with Carlos Ramos during the match against Naomi Osaka, with the official issuing her three code violations for receiving in-match coaching, smashing her racket and verbal abuse.

Speaking to the Sunday Times (h/t Alan Dawson of Business Insider), Federer said he felt Williams overstepped the mark in how she conducted herself.

"She went too far," the Swiss said. "She should have walked earlier. It's a little bit excusable. The umpire maybe should not have pushed her there. It's unfortunate but an incredible case study."

During the final—which Osaka won 6-2, 6-4—Ramos interpreted a gesture from Patrick Mouratoglou as coaching and penalised the 37-year-old; per BBC Sport, Mouratoglou acknowledged after the match that he was providing advice to Williams.

Williams told Ramos she would "never cheat" before she was issued another violation for smashing her racket, which also cost her a point and prompted the 23-time Grand Slam champion to call Ramos "a liar" and "a thief." That resulted in the umpire penalising her with a game, which gave Osaka a 5-3 lead in the second set.

Following the match, Williams said Ramos' actions were sexist. "He's never taken a game from a man because they said 'thief,'" she said, per BBC Sport. "But I've seen other men call other umpires several things. I'm here fighting for women's rights and for women's equality and for all kinds of stuff."

After the match, supporters inside Arthur Ashe Stadium made their feelings clear:

The United States Tennis Association fined Williams $17,000 for her actions that day.

In the same interview, Federer said it was unfair to ban Williams from wearing the catsuit she donned at the French Open and was also critical of the decision to issue a code violation to Alize Cornet at the U.S. Open for changing her shirt on-court.

"What was the problem with taking the T-shirt off or the catsuit?" he said. "Serena has worn crazier stuff in the past. Guys have worn crazier stuff. ... For me, it was a bit of nonsense. Just chill out for a second. I was totally on the women's side. Leave them alone."

Federer, a 20-time Grand Slam champion, enjoyed another strong year, winning the Australian Open early in 2018. He will be looking to finish his season on a high at the ATP Finals, which start Sunday in London.