All tennis athletes are schooled in the art of good sportsmanship. It's a really big part of learning the game. Serena knows what it is to be a graceful winner as well as lovely loser. Outside of using the unbearable heat all week as an excuse for bad behavior, it was more of an excuse for bad playing.
I think Serena was worried about this US Open Final match more than any other competition previously, not that she has always been a good sport before. I think she unfortunately felt, having gone through childbirth, in her case with a couple of hiccups, that she had to prove she could play and win and be a mother and therefore be what in her opinion was a miracle woman doing it all. I say good for her for what she has done, but also want to remind her it's ok to be normal, there are lots of women/mother heroes. It's ok to not always win, in fact to lose, and it's better yet to let a loss slide off one's back--to try again or to retire, whatever is one's choice. And no one ever said it would be easy for her or for any working mother in any job anywhere. We did not expect anything of her.
Technically it was Serena's coach, not her, giving the hand signals, he even admitted it on tv to Pam. But she saw them. He most definitely was telling her to move up on to the net and she did. Serena couldn't help but look in her coach's direction if she was standing in the correct set up position. And she heard the first offense ruling but I think tried to ignore it as if, well if I don't acknowledge it, perhaps it will go away.
As a tennis athlete, Serena knows the penalty for slamming and breaking one's racket, so no surprise there. #2.
The referee was 100% in line with the rules for the game penalty for the third offense, as with all of them.
There was no sexism here, sorry there was not. In fact Serena was caught with her hand in the cookie jar being a bad sport because she was losing and trying to bluff it off. Serena was losing and was trying to take the attention off the person who was winning and get it back on her. She hoped when things calmed down that then she could win. But her decisions all backfired on her. I believe she apologized to her opponent at the presentation when the horrible crowd wrongly booed as if Serena had been punished. What she should have said was, not there was sexism here, but rather you were the better opponent here, you deserved the win even without my loss of the penalty game. I was wrong to take attention from your excellent match. My behavior was bad, no atrocioous, I am sorry, and I apologize to you, to the umpire, referees, the crowd and tv fans.