Then, it was the verbal assault on the line judge, allegedly including death threats, after getting called for a controversial foot fault:
I can't really blame Serena Williams for being upset. It looks like the foot fault was an awful call. I won't even hold it against her that she smashed her racket. That's not even close to the first time we've seen a tennis player do that. I've actually seen players smash their racket when they're not even upset... they just want to grab a new racket, since they bring about a dozen of them to their matches.
However, her reaction was far beyond the realm of that which is acceptable, and while I don't necessarily agree with her subsequent point penalty on match point, I can at least understand it.
Tournament referee Brian Earley explained the situation:
"She was called for a foot fault, and a point later, she said something to a line umpire, and it was reported to the chair, and that resulted in a point penalty, and it just happened that point penalty was match point. It was a code violation for unsportsmanlike conduct."
It's an incredibly unfortunate situation for Serena, but it's entirely her fault.