Playing in Arizona, I ended up out in the desert—another errant tee shot—and I found that my ball was very close to a cactus. I had shorts on. So I took the towel off the golf bag and wrapped it around the leg closest to the cactus before hitting the shot.
That’s when my fellow competitor quickly informed me that I had violated the rules, citing the case of Kevin Stadler, who put the towel down on the ground to keep from getting his pants wet when he had to kneel on his knees to play a shot from under a tree.
Well, I thought getting two strokes added to my score is better than having to pick out cactus needles out of my leg. Just to make sure, I pulled out the Decisions on The Rules of Golf. To my surprise, I found the situation covered on pages 27 and 28 under 1-4/11.5—it was not a violation as long as I fairly took my stance, which I did. However, if I had placed the towel on the cactus, I would have had to add a two-stroke penalty. In match play, I would have lost that hole.
Looking at 13-3/2 cited by my opponent, I thought it was interesting that if I had wrapped a towel around my knees instead of placing it on the ground in playing from under a tree like Stadler that I would still have been penalized.
The difference? Getting your pants or knees dirty is not something that might be considered dangerous to you as getting cactus needles out would be.
Putting on my rain suit would work in both cases and would not be a violation of the rules.