Lucas Herbert produced a stunning round on Friday at Royal Birkdale, with the Australian going out in 28 and pushing on with more birdies on the back nine.
However, it was a moment at the par 5 14th which caught the eye of many, as Herbert's caddie, Nick Pugh, was seen using a rangefinder which, under The Open Championship's rules, is prohibited.
Finding the bunker with his tee shot at the par 5, Pugh pulled out the rangefinder to see if the ball had made it into, or cleared, the sand, with commentators on Sky Sports questioning the action.
"Something came to our attention not long ago. After Lucas Herbert hit, his caddie pulled out a rangefinder and was looking through it," explained Rich Beem.
Fellow commentator, Andrew Coltart, added "I have the rules out here in front of me on the rules sheet. Rule 10, prohibiting use of distance measuring devices, so we will need to clear something up very shortly."
A potential two-shot penalty loomed for Herbert but, thankfully, it was cleared up by Coltart, who stated: "To give you an update, The R&A ensures that batteries are removed so they can only be used as a binocular thing rather than a measuring device."
Essentially, Pugh was using the rangefinder as a way of seeing whether the ball had gone into the bunker, instead of measuring the tee shot that his boss had just hit.
Following on from the incident, Herbert would birdie the 16th to put himself nine-under-par for the round and championship.
On-course to make history, the current lowest round in an Open Championship belongs to Branden Grace, who fired an eight-under 62 at Royal Birkdale in 2017.
For Herbert, he left himself a five-footer to beat that score by one, but his par putt dived left and he tapped-in for an eight-under 62, becoming just the second player ever to shoot that number in a Major.
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Speaking after his round, Herbert's caddie, Pugh, stated: "My eyesight isn’t great – the glasses aren’t there to just make me look cool. I sometimes struggle when the ball comes down.
"I’ll use the rangefinder, which pretty clearly has no battery inside. It does nothing more than magnify. I checked, double-checked, triple-checked with the R&A and it's all good."
