He apparently purposely flicked the ball at a lineswoman who got hit in the throat and was disqualified.
People on Twitter are saying it was an accident. The footage isn't very clear but considering he's a top tennis player (Ie excellent control over the ball) and known misogynist it doesn't seem surprising he was angry and decided to take it out on a woman.
Particularly unimpressed by this BBC Sport tweet. How the fuck do they know it was "accidentally"? Aren't they meant to be unbiased?