In response to Serena Williams standing up against sexism at the U.S. Open, a racist cartoon portrayed one of the world's best-conditioned athletes as a fat, angry mammy character more suited to Gone With the Wind than the top tier of international tennis.

To underscore the point, cartoonist Mark Knight of the Herald Sun in Australia whitewashed Williams' U.S. Open opponent, Naomi Osaka, also a woman of color, portraying her as a waiflike figure with blond hair.

But this is nothing new for Williams. She's had a personal relationship with prejudice ever since her father, Richard Williams, pushed her and her sister Venus into the lily-white world of tennis. And the fact that it is such familiar territory for Serena is the very reason we must take her seriously when she says that sexism in tennis is real.

The incident in question, when Williams confronted chair umpire Carlos Ramos after Ramos accused Williams of cheating by getting coaching during the match, was one of many flash points in her storied career.

Since taking her first swing as a pro at age 14, Williams has won 23 Grand Slam titles, become a fashion icon, and embraced the part of spokeswoman and role model for young women coming behind her.

Ironically, one of those young women was her opponent at the U.S. Open — Naomi Osaka. That's part of what made the incident with the chair umpire so ugly.

"It's unbelievable, every time I play here, I have problems," Williams said after the chair umpire accused her of cheating. "I did not get coaching, I don't cheat. You need to make an announcement. I have a daughter and I stand for what's right for her. You owe me an apology.

"For you to attack my character is something that is wrong," Williams said. "You will never, ever, ever be in another final. You are a liar."

Eventually, Serena called Ramos a "thief" for taking away a point from her. In response, he gave her a code violation for verbal abuse, resulting in the game penalty that gave Osaka a 5-3 lead in the second set.

Taken in isolation, it would seem that Williams overreacted. But to understand why she Williams responded as she did, you have to understand that Serena wasn't always the top tennis player in the world.

In fact, she wasn't even welcome on the court.

Before she became one of the best-known athletes in the world, Serena Williams — a little black girl from Compton, Calif., with beaded braids and a killer swing — had to battle both racism and sexism as she clawed her way to the top.

She was verbally abused by white audiences in America and beyond. Her father was accused of fixing matches between Serena and Venus. Fellow tennis players spread rumors to make it worse.

Things got tense at a tournament called Indian Wells in 2001. Here's what Serena's father told USA Today.

"When Venus and I were walking down the stairs to our seats, people kept calling me 'nigger,' " Richard Williams said. "One guy said, 'I wish it was '75; we'd skin you alive.' That's when I stopped and walked toward that way. Then I realized that [my] best bet was to handle the situation nonviolently. I had trouble holding back tears. I think Indian Wells disgraced America."

That tournament, with people cheering wildly every time Serena made a mistake, was just one example of the racism she faced while fighting her way to the top.

But Serena faced sexism, too. As one of the top players in tennis, she had to fight the tennis world to make sure that she and other women were paid as much as men. When she took off for maternity leave, she was stripped of her No. 1 ranking, even though players kept their ranking when they took time off for injuries.

So Serena knows sexism when she sees it. That's why when she accused the umpire of being a thief for taking away a point because she had been arguing, and he then gave her another penalty, Serena said, "You wouldn't do this if I was a man."

She had a point. John McEnroe routinely argued with refs when he played tennis, and while he was fined more than $80,000 over the course of his career, he got commercials and endorsements celebrating his arguments with officials. In fact, people came to see him argue. It was part of the show.

Yet somehow when Serena does it, it's offensive. It's not ladylike. It's wrong.

Well, I say it's wrong to dismiss Serena's complaints as if she's crazy. I say it's wrong to treat women like second-class citizens. I say it's wrong to pretend Serena doesn't know sexism when she sees it. Because if anybody knows discrimination after facing it most of her life, it's Serena.

Solomon Jones is the author of 10 books. Listen to him weekdays from 10 a.m. to noon on Praise 107.9 FM. @solomonjones1