After the problems arising for Mickelson striking a moving ball in the U.S. Open, I think you should see this funny/interesting video (Facebook):
The question is, whether or not the player incurred two penalty strokes under Rule 14-5 for playing a moving ball?
Well, the Rules of Golf does not define when a ball is “moving”, but only when it has “moved”.
Two things could be considered:
1) Decision 18/3 states:
Q. A ball rests in the fork of a branch of a tree. The player climbs the tree to play his next stroke. The branch bends under his weight. Although the ball has moved relative to the ground, it has not moved relative to the fork. Is the ball deemed to have moved?
A. The ball is deemed not to have moved since it did not move in relation to the fork of the tree in which it was lodged.
2) The Definition of “Move or Moved” states: “A ball is deemed to have “moved” if it leaves its position and comes to rest in any other place.” Maybe you can from that conclude, that the ball needs to leave its position to de deemed to be moving.
My interpretation would be that the ball is not moving, because it does not move in relation to the branch on which it lies in/on.
Therefore it was an (excellent!) stroke and the player incurs no penalty.