You’re in a greenside bunker with a slope up to the green. You hit a good-looking shot nicely on line, then grab the nearby rake to smooth out the rather prominent footprints you’ve left.
Unfortunately, your shot perches at the top of the slope, then begins to roll back - slowly at first. It gathers speed down the slope, and finishes back in the bunker, almost exactly where it started.
The raking you did is clearly going to make your next shot substantially easier than it would have been had you waited. Have you committed a foul by doing this?
Yes, because you have changed the lie of your ball. The exact circumstances don’t matter.
As written it sounds like the ball moved on its own, rather than the golfer moving the ball. Does that not matter? Would you get a penalty in any situation where an outside force moves the ball?
According to my golfer spouse, it’s nuanced and the rules about bunkers have changed. But his instinct is yes it’s a foul, since the ball never stopped moving.
ETA He just looked something up. So as long as you’ve completed your part, you’re ok, even it renters the bunker or didn’t stop moving.
Rules Guy article in Golf magazine, 2020.
Golf is a strange sport in terms of rules. In a tournament years ago, Craig Stadler was informed that he had violated rule 13-3, illegally building a stance by using the towel to keep from muddying his trousers . The two-stroke penalty meant he had signed an incorrect scorecard on Saturday and he was disqualified.
What made it even more amazing is the fact that the call was not made by any official at the tournament. It was TELEPHONED IN BY A FAN, thus starting 30 years of TV viewers actually being allowed to officiate golf tournaments from their living rooms at home.