Stefanos Tsisipas nearly did something that cost Djokovic the
US Open a few years ago and that's hitting somebody on the court with a tennis ball as he nearly avoids disqualification.
A few years ago Djokovic was disqualified from the US Open after hitting a court umpire with a tennis ball and Tsitsipas nearly did the same. He was up 2-0 on Lehecka when he slammed a ball into the wall out of frustration and nearly hit a ball kid. He avoided that by mere seconds and centimetres with John Courier, who commentated on the match, explaining what would have happened if actually hit the ball kid.
People have been hit by balls on the court before but players get excused if it happens during play. When it happens away from a play, and when the action was clearly reckless then players get punished. Considering the score it would be catastrophic. He did something similar at Wimbledon and nearly hit a spectator.
Check it out below.