A penalty imposed under the new rules introduced at the start of the year has been rescinded just over 24 hours later.
American Denny McCarthy was hit with the punishment in the second round of the PGA Tour’s Waste Management Phoenix Open on Friday.
He was penalised by two shots under Rule 10.2b(4), which does not allow caddies to stand behind players as they line up their shot.
However, a review of the incident has led the R&A and the USGA to conclude that the penalty should not have been applied.
In a joint statement, the game’s two ruling bodies said: “Following an ongoing dialogue with players and in co-operation with the PGA Tour rules team, the R&A and the USGA revisited the penalty assessed to Denny McCarthy during round two of the Waste Management Open.
“After an additional review of available video (on Saturday) morning, it was determined that the penalty would not apply in this instance nor in a similar instance involving Justin Thomas.
“In each of these cases, when the caddie was standing behind the player, the player had not yet begun taking the stance for the stroke, nor could useful guidance on aiming be given because the player was still in the process of determining how to play the stroke.
“The same would be true for any similar situation that might occur.”
The R&A and the USGA said clarity on how to appropriately apply the rule was needed and that they “will provide the necessary clarifications in the coming days”.
During last week’s Omega Dubai Desert Classic, Li Haotong was penalised two shots because his caddie was on a direct line behind the ball when he began to take his stance on the green.
European Tour chief executive Keith Pelley expressed his concern at the “grossly unfair” penalty, which meant defending champion Li dropped from a tie for third to a tie for 12th, costing him more than £70,000.
But, after reviewing Li’s case, the R&A released a statement last Monday saying the referees had correctly applied a two-shot penalty in that instance.
The McCarthy decision led the European Tour to issue advice to players before heading out for today’s final round of the Saudi International at Royal Greens.
Referring to Rule 10.2b4, senior referee Andy McFee said: “We have been advised overnight by the R&A of an immediate change of interpretation within this rule intended to clarify when a player will be in breach.
“Beginning the stance to take a practice swing close to the ball has been removed as a point of breach.
“The position of the caddie when the player BEGINS to takke the stance for ‘the stroke’ remains criticial. The caddie cannot be deliberately standing on or close to an extention of the line of play behind the ball for any reason at this moment.
“Other tham on the putting green, it continues to be true that there is no way out of this penalty by backing off the stance already taken.
“The first foot placed in position for the stance for the stroke remains the key point and the caddie must be well away at this moment in time.
“The best advice remains that the caddie standing directly behind the player is a dangerous practice and should be avoided at all times.”