Novak Djokovic was disqualified from the US Open after hitting a lineswoman with a ball during his clash with Pablo Carreno Busta.
The Serb, who had previously been suffering with a shoulder injury, was visibly frustrated after being broken in the first set as the Spaniard took a 6-5 lead.
Nadal says he was 'put in his place' by Rublev loss
He struck a ball away in frustration - and although he was not facing the assailed lineswoman, the ball hit her and she was bent double, coughing and needing medical attention.
There then followed a lengthy consultation with the tournament referee, with Djokovic seemingly attempting to convince the referee and chair umpire to let him continue in his campaign but to no avail.
The ITF's Grand Slam rule book reads: "Players shall not at any time physically abuse any official, opponent, spectator or other person within the precincts of the tournament site...
"For the purposes of this Rule, physical abuse is the unauthorised touching of an official, opponent, spectator or other person.
".... The Referee in consultation with the Grand Slam Chief of Supervisors may declare a default for either a single violation of this Code or pursuant to the Point Penalty Schedule set out above."
There is precedent for a player being defaulted from events for striking one of the match officials, with the most recent example being a young Denis Shapovalov hitting the chair umpire while representing Canada in the Davis Cup.
A young Tim Henman hit a ball girl with a ball while playing alongside Jeremy Bates in Wimbledon doubles action and was subsequently disqualified in 1995, and David Nalbandian was defaulted from the Queen's Club final in 2012 after kicking the advertising hoarding and hitting a line judge.
Djokovic's elimination means that there will be a first-time men's singles winner since Stan Wawrinka won the Australian Open in 2014. Rafael Nadal and Wawrinka elected to skip the tournament, while Marin Cilic and Andy Murray have been eliminated. Juan Martin Del Potro and Roger Federer are both long-term injury absentees.
"It's the right decision," Tim Henman said.
He is not aiming for the line judge, but has hit the ball away and you have to be responsible for your actions.
'Very challenging' - Djokovic: Most players experiencing mental and motivational issues
'I fell into a hole' - Thiem opens up on difficult start to season