A careless breach of the rules by Rory McIlory earned him a two-shot penalty and cost him a share of the halfway lead in the Abu Dhabi Golf Championship.
Northern Ireland's US Open Champion would have been alongside Dane Thorbjørn Olesen but for brushing sand away from his line on the ninth hole of his second round.
That would have been all right if it had been on the green, but he was six feet off the putting surface and World Number One Luke Donald instantly brought it to his attention.
"I wasn't thinking clearly and just made a very stupid mental mistake," McIlroy said following a level par 72 that left him tied for fourth on five under par and part of a group which also included Tiger Woods.
Asked if he did not know the rule or just had a loss of concentration he added: "I think it was a little bit of both - first week back as well.
"Luke said 'Don't think you can do that' and I was like 'Oh yeah, I can't, can I?'
"It happens and you just have to take it on the chin.
"There was so much sand in my line I didn't even think about it. I'll definitely not do it again."
Olesen carded a brilliant five under par 67 to lead the Abu Dhabi HSBC Golf Championship, but the 22 year old Dane has a host of big names right behind him going into the weekend.
