The USGA, in conjunction with the R&A, has ruled on Jordan Spieth's lingering question from the WGC-Cadillac Championships over whether or not he could wet his putter to help him gain traction on the slick surfaces at the Trump-Doral course.
"We have definitive position that is held by both the USGA and the R&A that this is a breach of Rule 4-2a for purposely changing the playing characteristics of a club during the round," senior director of Rules of Golf & Amateur Status Thomas Pagel told GOLF.com. "This was confirmed in the days following the question that was raised by Jordan."
On the course, USGA officials advised Spieth—after he stumped his playing companions, on-course rules officials and broadcast analysts—that, for the time being, he shouldn't intentionally add moisture to his putter by licking his finger (or the putter). But that if he wiped the putter with a towel that happened to be wet, there would be no violation.
Often caddies carry damp towels to clean the ball and the clubs of Tour pros, so wiping a putter with a towel wouldn't otherwise be out of the ordinary.