Jockey Aidan Coleman has been banned for four days for using his whip above the permitted level when winning last month's Welsh National.
No action was taken on the day against Coleman, 26, by stewards at Chepstow Racecourse after he won on Emperor's Choice, trained by Venetia Williams.
An inquiry was held by the British Horseracing Authority on Saturday.
The decision to take retrospective action has been criticised, although Coleman says he will not appeal.
"I'm happy with what's happened and that was the margin of error and it's done," he said.
Coleman won praise on the day for his winning ride, including from the BHA's outgoing chairman Paul Bittar.
But his organisation decided to take action after footage of the race was reviewed.
"As with other sports there is the capacity for inquiries to be held retrospectively into offences which are not dealt with by the officials on the day," said BHA spokesman Robin Mounsey.
"If the BHA identifies a potential breach of the rules it has an obligation to hold an inquiry into it."