I marked my ball, on the putting green, with a ball-marker, lifted the ball, and moved away to the edge of the green. On returning to play my ball I found that the ball–marker was no longer on the green. I had accidentally stood on the marker and it was stuck to the bottom of my shoe. Do I incur a penalty?
You incurred a 1 stroke penalty under Rule 20-1. This requires that the position of the ball must be marked, before it is lifted, and that it must remain in position until the ball is replaced.
The ball must be placed as near as possible to its original spot.
A similar penalty would be incurred if the ball-marker were accidentally kicked.
If your fellow competitor kicked the marker they would incur the penalty.
If however when you placed the ball marker in position you pressed it down with your putter and it stuck to the sole of your putter you would not incur a penalty as the movement of the ball-marker was directly attributable to the specific act of marking the position of the ball. Again the ball must be placed as near as possible to its original spot.