There are a few rules that apply to most billiard games that will determine legal or illegal shots. Some of them you may have already read about in this book, but let's get more specific now.
To hit a legal shot in a game means:
You can touch the cue ball only with the cue tip.
You can only strike an object ball with the cue ball.
You can only hit the cue ball once per shot.
The cue ball must strike the correct object ball (depending on the rules of the game).
An object ball must touch a cushion or land in a pocket after it is struck by the cue ball, or the cue ball itself must touch a cushion (depending on which game you are playing). In other words, when you strike the cue ball into an object ball, the goal is to land it in a pocket.
If it doesn't go into a pocket, either the object ball or the cue ball should at least hit a cushion to be a legal shot. Even if you hit several object balls, as long as one of them hits a cushion, the shot is legal.
Whether a shot is legal or illegal has much to do with the game you are playing. Eight ball and nine ball, for example, have different rules regarding the order in which object balls must be struck. You'll read more about that later on.
Call shots are used to take luck out of a game. When a game is declared a “call shot” game, each player must announce which ball he or she will strike and the pocket into which the ball is going.
While some games (games you play with friends or in a local bar) are casual and only have the stipulation that you must pocket one of your own balls (a striped or solid ball), other games will be declared call shot games at the onset. This puts a little more challenge into the competition.
If you miss your shot in a call shot game, it means you either didn't pocket the ball you said you were going to pocket, or you pocketed the ball but in the wrong pocket, or you didn't pocket the ball at all. If any of these circumstances occurs, your turn at the table will end, but you won't incur any penalties.