Denis Shapovalov was playing a match against Kyle Edmund when he got frustrated after losing a point. He smashes a ball with his racket, but not paying attention to where he’s hitting, it goes right at the umpire who takes it in the face.
That’s one reason to keep your eye on the ball, both if you’re a player and an umpire. Shapovalov was then disqualified from the Davis CUP, but it really looks like some bad luck and a flared temper. I mean, what are the odds?