Furious at the decision, Kyrgios booted a water bottle and then stunned spectators by picking up a fold-up wooden chair and hurling it across the court before picking up his bag and storming off, although he did shake hands with Ruud and the chair umpire.
"Very eventful day to say the least," Kyrgios wrote on Instagram later. "Emotions got the better of me and I just wanted to say that the atmosphere was crazy out there today, just super unfortunate that it had to end in a default. Sorry Roma, see you again, maybe."
It was later confirmed Kyrgios didn't simply choose to leave the arena, but exited after being defaulted by supervisor Gerry Armstrong.
The match was subsequently awarded to the world No.76, who'll now face Juan Martin del Potro for a place in the quarter-finals.
Ruud called for the ATP Tour to come down hard on his opponent. "I'm sure I'm not the only one who thinks he should be suspended for at least half a year," Ruud said.
Serial offender Kyrgios, who has a history of bad behaviour, was suspended by the ATP Tour in 2016 for tanking in a match against Mischa Zverev and insulting fans during a loss at the Shanghai Masters.
The ATP have confirmed Kyrgios will lose $33,635 in prize money from the tournament in addition to 45 ATP points, and said there's likely to be further punishment pending an investigation.
In 2015, Kyrgios insulted Stan Wawrinka with crude remarks during a match in Montreal.
He was fined $US12,500 and given a suspended 28-day ban.
He also attracted criticism for deciding not to play at the 2016 Olympics because of a spat with chef de mission Kitty Chiller.
