The R&A and the USGA have recently been asked about methods of reading a putting green where players stand astride or stand or walk alongside their estimated line of putt to assess the slope of the green and the break of the putt. The question is whether such actions have the potential to breach Rule 16-1a.
Under Rule 16-1a, the player must not touch the line of putt. (There are exceptions to Rule 16-1a, but none of them relate to methods of reading the putting green or determining a line of putt.) The “line of putt” is defined in the Rules as “the line that the player wishes his ball to take after a stroke on the putting green” including “a reasonable distance on either side of the intended line”. The penalty for a breach of Rule 16-1a is loss of hole in match play or two strokes in stroke play. Consequently, players who use such green-reading methods should take care to avoid walking on their line of putt in order to avoid the risk of penalty under Rule 16-1a.
The same is true of any other practices used by players to gain information when their ball is on the putting green, such as walking alongside the line of putt to measure the distance to the hole or standing at a midpoint to the hole and hovering the putter over the line of putt. To avoid the risk of penalty, players or their caddies who take any such actions should take care to avoid touching the line of putt, which includes a reasonable distance on either side of the intended line, with their feet, the club, or anything else.