During the second round of the WM Phoenix Open, Xander Schauffele had a par putt to hole on the par 4, 11th. While he and his caddy, Tech, looked over the putt from all angles, Tech went near the hole and used his shadow to draw an imaginary line from the ball to the hole. Schauffele proceeded to match the arrow marking on his ball to the line of Tech’s shadow.

It first struck me as odd, because I’d never directly seen a caddy do this. As I understood it, a caddy cannot touch the ground of a players line of putt or use an “artificial aid” to do so. Call the Rules Police! I shouted in my head.

But was it a rules violation?

Before I get to that, it goes without saying that Schauffele is a top-ranked golfer on the PGA Tour, having won the Olympic gold in last years summer Olympics and holds several PGA Tour titles. Tech, is a close friend who is also an accomplished player and was filling in for Schauffele’s regular caddy. Surely, these guys know and play by the rules, right?

I consulted the powers that be through the magic of search, and came upon this post over at Golf.com, written over two years ago: “Is using the shadow of the flag for putting alignment illegal?”

In this instance, a golfer asked:

“I had a four-foot putt exactly on the line of the flagstick’s shadow, so I left the pin in and made the putt. My playing partner called foul. I know the USGA changed the rule so that it’s the player’s choice whether to leave the stick in or out, but does that still hold when using its shadow as a beacon?”

According to Golf.com’s rules guy, this is perfectly legal. Of course, this wouldn’t work on a curving putt, but if you have one of those tricky (yes, tricky) straight putts, it could do you some good to use the aid of a shadow.

It’s something I’ve never thought about – because straight putts seem fairly rare.

Use it to your advantage next time you’re out on a sunny day, with your caddy! Or pin in the hole.