[golfer]

Grounding your club in a bunker would potentially allow you the advantage of knowing how firm or soft the sand is, as well as how deep.

From an article at ESPN.com, rules official David Price knew Johnson was in a bunker when he hit his 2nd shot, he was just unaware Johnson had grounded his club.

"Price said he went up to Johnson as he was preparing to hit his second shot and asked him if he needed anything. Johnson replied that he needed the crowd moved to the right, so Price went to make sure that was being done and then waited on the fairway. He never saw Johnson ground his club.

But Price had dealt with two other questions from Johnson or his caddie about bunkers the previous few holes. On No. 14, Johnson hit into an area just past a bunker and asked if he could take some practice swings for that shot in the bunker. Since the ball wasn't in the bunker, Price told him he could. Then, on No. 16, Johnson's caddie asked if he could remove some stones near the ball. Price told him they were in a bunker and by rule they can move loose impediments as long as the golf ball doesn't move. But there was no doubt to Price that Johnson was in a bunker.

"All he had to do was ask," Price said. "He'd asked me before that. He'd been in a bunch of bunkers. You don't remind a player on every hole that you can't ground your club."

Price said the bunker on No. 18 that Johnson was in was formed like many other bunkers on the course.

"It was a rather small one, but it was an area that had been dug out and filled with sand," Price said. "The only thing that made it different than previous bunkers is that he hit the ball so far offline, it was in a bunker that had been trampled down instead of one that was finely raked. We told players on the information we gave them that all sand on the course was considered a hazard, even if there were footprints or tire marks."