Golf is unique among sports in that it relies on players to call penalties on themselves. While professional tournaments will have officials on hand to help spot violations and clarify rules, for local players, the onus is on the player to know and obey the rules of the game.
When struck off of the face of a golf club, a ball is expected to be allowed to travel along its driven path without obstruction as a result of the actions of a player, be it the player that struck the ball or one of the other players in the group. A golfer can fall victim to a two-stroke penalty if she fails to properly monitor the location of the flag when on the green, and the ball accidentally strikes it. The penalty applies whether the flag is in the hole and has failed to be removed, or if the flag was removed, laid down, and then the golfer strikes it accidentally with a putt. A golfer can be penalized two strokes if he interferes with another player's shot by hitting the ball or causing something else, such as a club or bag, to hit the ball.
Ball Location Penalties
Proper marking of a ball is essential, whether it involves marking a ball's position on the green or the unique markings drawn on a ball to identify it. A player who plays a ball that isn't hers is subject to a two-stroke penalty. This rule does not apply in a hazard, such as a bunker, where a buried ball cannot be properly inspected. A player can also be penalized two strokes for playing his ball from the wrong location. This occurs most commonly on the green, when a player moves a ball mark out of another player's line, then forgets to move it back before replacing the ball.
Hazards can also subject players to two-stroke penalties if a player is not careful. Placing the club head down in a bunker, unless it is in the act of striking the ball, results in a two-stroke penalty. A golfer is similarly penalized two strokes for striking a loose impediment in a hazard with their swing, such as nearby reed if striking out of a shallow water hazard.