Larry and Scott were both on the green in regulation, a rare occurrence. Larry was away. He asked Scott to move his ball mark a couple of putter heads to the right as it was in his line of putt. Larry’s 11 foot putt went in for birdie. Scott set his ball down, lifted his marker and putted. His ball also dropped into the cup. Never before had these two made birdie on the same hole at the same time. Of course Scott was elated. But just for 10 seconds. Larry pointed out to Scott that he had not moved his ball marker back to its original position, meaning Scott had putted from the wrong place.
Larry said, "that will be a one stroke penalty and you will have to put again, this time from the correct position."
Of course, this is when the fun began. Larry was accused of setting the scene trapping Scott into making the error. Scott then argued that there really should not be a penalty as he was accommodating a fellow competitor and he had not gained any advantage.
What is the correct ruling?