The R&A

Ball at rest moved or lifted - Deciding what caused the ball to move

If it is known or virtually certain that your ball moved, the Rules recognize only four possible causes for your ball at rest to move before you make a stroke:

Natural forces, such as wind or water,
Your actions, including the actions of your caddie,
Your opponent’s actions in match play, including the actions of your opponent’s caddie, or
An outside influence, including any other player in stroke play.

You, your opponent or an outside influence are treated as having caused the ball to move only if it is known or virtually certain to be the case. If not, the ball is treated as having been moved by natural forces.

Related Rule - 9.2b