David Nalbandian was disqualified from the Aegon Championships final at Queen's after kicking an advertising board into line judge Andrew McDougall.
Here, BBC Sport pundits and the world of tennis react to the Argentine's behaviour, which gifted Marin Cilic victory and the title.
David Felgate, Tim Henman's former coach
"There was no intent to hurt but he took a right foot to that like a penalty kick.
"It is like when players have thrown racquets. Xavier Malisse got defaulted in Miami some years ago when he hit a line judge.
"It is the same situation as when Tim Henman hit the ball and hit a ball girl as she ran across the court."
Pat Cash, former Wimbledon champion
On Twitter: "Awkward for Nalbandian as he's letting out steam. What a pity for all."
Chris Kermode, tournament director
"It is obviously not the way that we wanted to finish the final and I can understand the crowd's frustration.
"But the tournament is governed by ATP rules and this was a clear-cut case.
"The line judge was seen and treated by St John's Ambulance. He also saw the doctor, and no further treatment was required."
Ivo Karlovic, world number 56
On Twitter: "What's the penalty for kicking the chair in the real world?"
Sue Barker, BBC Sport
"I am not sure I have ever seen anything quite as brutal as this. It was an accident, but he is a fiery character and we have seen this.
"We thought it would be nice to give David the chance to say sorry to the fans for seriously injuring someone, but instead, he turned it into a battle royale."
Fernando Verdasco, world number 16
On Twitter: "I have never seen anything like it in my life. He wanted to kick the board, not the line judge. It was an accident in my opinion."
Tom Barnes, ATP supervisor
"It is unsportsmanlike conduct, and the supervisor has the authority to declare an immediate default. Once I saw that the line judge was injured, I didn't have any other option."
Andrew Castle, BBC Sport
"It's a desperate way for this to end and the crowd hate it. David Nalbandian will be ashamed of himself and he should be of that, in a way.
"But in another way, he is unlucky. He will apologise and he will be upset, but he's messed up there.
"What a rotten way for this to end. I hope the line judge is OK.
"He went rolling off his chair and clearly that hurt him. He was bleeding from the shin. This is just not on, even if it was an accident."
Neil Harman, Times tennis correspondent
On Twitter: "Nalbandian apologises, but is not happy with the ATP. The rule book is very big, he says. Blames the ATP but has to look at himself."
John Lloyd, BBC Sport
"I do not know how he will explain that one. He just went way overboard.
"As soon as he did it, he knew it was all over as he quite rightly should have been."
Mike Dickson, Daily Mail tennis correspondent
On Twitter: "Sober analysis is that there was no option but to default Nalbandian. The linesman's shin was covered in blood."