I think the initial problem was the penalty for coaching. I don't watch enough tennis to be able to tell whether other players get away with similar coaching (and if so is it something women are penalised for more than men) ? Could you tell from the TV coverage or would you have to be there? - the latter I'd have thought. Also is this umpire stricter than some of the others we've heard about ? In which case it's about inconsistency in officials, which let's face it we know all about in football.
Then there's her outburst and accusing him of being a thief. It's one of those extraordinary outbursts that will be replayed for many years in the same way as McEnroe's "you cannot be serious" line is still remembered. I'm pretty sure a man who'd had a similar ballistic outburst would have been equally penalised.
And I think it's ironic when people say that "middle-aged white men" aren't allowed to express an opinion on topics such as sexism. Thereby taking a view that discriminates on the basis of sex, age and race. Would it be ok to say that black women can't express an opinion on any given topic due to their sex/race ? Of course not. Because that's a sexist and racist attitude. Which should apply equally to all sexes, races and ages.
The fact that white men, by and large, suffer less from discrimination in the UK currently is irrelevant.