"But her expectations that the Williams sisters should be friendly and non-threatening do veer very close to racist territory"
But did she say that? I get the point your making, it's similar to the line of "I don't mind gays, I just don't want it shoved in my face" I.e. I'll tolerate that minority but they better act right and appreciate me allowing them to do X.
But if this is the post you're calling the posted up on
" yes v aggressive but that's not a bad thing in sport.they are just not v pleasant personalities.some of the players are v engaging and smiley, friendly.the sisters are not like that."
Then I don't think that it falls into the category described. The poster never said they should act a certain way or not be allowed to act the way they do.
She's described them as unpleasant and nothing more, based on their court actions.
She hasn't said that they should be no threatening or smile to appease her or the crowd, she's just stated that they don't do it at present and she finds them unpleasant.
Similar criticism plagues sports men and women of all ethnicities. Ronaldo, a white male, who's generally accepted to be the second best player in the world is loathed by many for perceived arrogance and a dismissive attitude to team mates.
Wayne Rooney for his thuggish image.
Their defenders will say the same things that I'd defend the Williams sisters with. They're not paid to be nice or he role models, they're paid to win. But that doesn't mean people can't dislike those facets of their personality and hope others who they do like win out.