Never doubt or think you've beaten Roger Federer. That's the lesson learned Marinko Matosevic playing the Swiss man in the US Open yesterday.

Matosevic made the mistake of turning his back on the champion and had started to walk back to the baseline, missing Federer's trademark genius and this between-the-legs return which then slapped right on the ass, which gave Michael Jordan and everyone else in attendance a kick.

Here it is again in GIF form, because it's definitely worth a second, third and forth look.

Via YouTube/Twitter