A guide to the rules of golf

Play the wrong ball and you'll end up in trouble

It is very important to make a note of the make and number of the ball you are playing.

Most professionals take the added step of marking their balls with a pen.

Playing the wrong ball can result in a two-shot penalty.

You are allowed to pick up your ball during the course of play in order to inspect it to see if it is yours, except when it is in a hazard.

But you must mark it first and replace it exactly as it was afterwards or incur a two-shot penalty.