The child (look for him on the left side of the clip) apparently thought the point was over and ran onto the court to collect the ball while Troicki was winding up for an overhead slam. They almost collided before the chair umpire called a let and forced the point to be replayed:
Calling the match on The Tennis Channel, John McEnroe suggested that Murray should have done the sportsmanlike thing and given Troicki the point since it seemed like Troicki would have won if not for the Bartman-like interruption. (Just like the volatile Johnny Mac would have done during his playing days, I'm sure.) That would have been nice to see, but you can't hold it against Murray for keeping his mouth shut while chair umpire Pascal Maria explained that the point would be replayed. Choosing not to make the most sportsman move doesn't make one unsportsmanlike.
Any sympathy you may have had for Troicki was lost a few points later. After Murray won a point on a similar overhead winner, Troicki mockingly asked the ballboy why he didn't run out during that point. Then he kicked the ball away from him. Little tip, Viktor: Showing up an 11-year-old is never the way to get a crowd on your side.
The point ended up not mattering in the end. Troicki would lose the replayed point but broke Murray in that game, en route to a 5-2 lead in the decisive set. On his serve at 5-3, the Serb went up 30-0 and was two points away from winning the match before falling apart and losing the next five games.
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