The general rules governing the game of billiards are more or less the same universally with certain exceptions.

Racking of ball

Balls must be racked using a triangle of specific dimension, with the apex ball at the foot spot and all other balls following it and making contact with each other.

Legal shots

The shots that qualify as legal are only those where cue ball should be struck with the cue tip.

Pocket a ball

The opponent gets to strike when the player fails to pocket a ball.

Lag for break

This rule is used to determine which player gets to play the opening shot. Balls of same weight and size, cue balls or non-stripe object balls are shot by both players at the same time, one from the right and other from the left of the head spot, to the foot cushion and back to the head end of the table. The ball that is nearest to the head cushion is considered as the winner. The balls shot for lagging should touch the foot cushion of the table at least once. There are various shots that are considered as loss of lag like when the ball jumps out of the table, crosses to the opponents half, falls into the pocket or touches the long side of the cushion etc.

Opening break Shot

A lag shot or lot is used to decide on which player can play the opening shot. A lag is usually used in formal tournament or competition.

Cue ball on opening break

A game is considered open as soon as the balls are positioned and the cue ball struck with the cue stick across the head string.

Deflecting or stopping the cue ball after the opening break has been shot is considered foul and the opponent qualifies for the shot.

The cue ball in hand rule is applied in certain games where the opening shot is administered or an incoming player penalizes the player.

Rules when a ball is considered pocketed or otherwise.

The location of a ball is verified by where its base (or center) rests.

Both feet must be in contact with the floor when a shot is struck.

Shooting any ball in motion is considered foul play.

A stroke is deemed to be complete only when the entire ball has stooped moving.

The area that is behind the head string is not the head string, hence an object ball right on the center of the head string can be shot at by the cue ball.

The way foul is penalized may differ but there are certain general rules like innings ends for foul players.

If the cue ball doesn’t contact the object ball at any shot it is considered foul.

Touching or moving any balls other than the cue ball when the shot is played, or scratching of the cue ball or pushing (not striking) the cue ball is considered foul.

Any damage to the equipment used weather accidental or otherwise is foul.

Unless specified by the game it is considered foul if the cue ball jumps in shot.

A ball is considered to have jumped unless it returns to the cushion of the table on its own.

These are a few of the exhaustive list of rules of billiards.