Whether it’s wind, a playing partner, or your own foot — what happens next depends on who or what moved the ball. Here’s the rule explained clearly.

If your ball moves before you play it, the first question to ask is simple: what caused it to move?

The Answer

The basic principle is this — if your ball moves, you must replace it. Whether you’re penalised depends on the cause.
You caused it to move — one stroke penalty, and you must replace the ball on its original spot. The exception is on the putting green, where accidentally moving your ball carries no penalty at all. Replace it and play on.
Wind, water or gravity moved it — no penalty. Play it from wherever it ends up.
An animal, spectator or outside influence moved it — no penalty to anyone. Replace the ball and play on.
Another player moved it (stroke play) — no penalty to you. Replace the ball.
Your opponent moved it (match play, away from the green) — one stroke penalty to them. Replace the ball.

Rule Reference

The R&A / United States Golf Association
Rule 9.4 — Ball Lifted or Moved by Player
Rule 13.1d — Ball or Ball-Marker Moved on Putting Green