You may change your ball before playing your tee shot, but it is good practice to advise a player in your group if you are changing your ball.
Play your tee shot from between, and not in front of, the tee-markers. You may play your tee shot from up to two club-lengths behind the front line of the tee-markers.
If you play your tee shot from outside this area:
- in match play there is no penalty, but your opponent may require you to replay your stroke provided he does so immediately;
- in stroke play you incur a two-stroke penalty, the stroke itself does not count and you must play a ball from within the correct area.