Ronnie O'Sullivan took off his shoes mid-match at the Crucible on Tuesday - but still socked it to debutant Craig Steadman.
The Rocket raced into a 7-2 lead in his first match at this year's Betfred World Championship in Sheffield. But five-time champion O'Sullivan, 39, could now face a fine after breaching snooker's strict dress code against the 32-year-old from Manchester.
O'Sullivan almost made a 147 maximum break in the first frame - missing the 14th red on a run of 104. But he played the sixth frame in his socks after removing some new shoes, complaining about a painful big toe.
O'Sullivan saw his lead pegged back to 4-2 after losing that frame - and tried to hand his footwear to a fan. He also asked: 'Does anyone in here have some size eight or nine shoes I can borrow. I'm serious?'
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But tournament director Mike Ganley summoned him out of the arena and lent him his own shoes for the last three frames of the session.
The WPBSA dress code reads: 'Each member shall ensure that their dress and appearance is smart and appropriate for a professional player.' O'Sullivan was given dispensation to wear casual shoes last year at the UK Championship after breaking his ankle.
World Snooker chairman Barry Hearn said: 'The one thing you can be sure of with Ronnie O'Sullivan is that you have absolutely no idea what he is going to do next.
'I would rather he played with his shoes on if it all possible though. And what happens if his trousers are a bit tight in the next session of his match?'
Meanwhile, Ding Junhui blew the chance to win £30,000 and become only the seventh player to make a maximum at the Crucible. He incredibly played for the blue after the 13th red following 12 blacks and only gasps from the crowd alerted him to the blunder.
Ding looked stunned before a doomed long-distance attempt on the black failed. However, he shrugged off the setback to claim a 10-7 victory.