A free ball in snooker
is awarded when a player commits a foul which leaves the other player snookered. A player is snookered when he cannot see the ball on
or balls on
; that is, he is unable to hit a direct stroke
in a straight line
to the either extreme edge
of any ball on because of obstruction
by a ball not on.
The player nominates the free ball, and for the duration of that shot, the free ball is regarded as the ball on; it assumes the value of the ball on, and any fouls involving it are penalised at the same rate as the ball on, unless of course a ball of higher value than the ball on is also fouled.
Say for example that the reds are on, after a player tries to snooker his opponent by playing the cue-ball up behind the black, but fails to make contact. This is a foul stroke, and as a result of the cue-ball's position, the in-coming player is snookered. The in-coming player can then claim a free ball, and he nominates one of the colours. Then, for the duration of that shot, the nominated ball is regarded as a red; potting it scores one point, and the player's next shot will be on a colour. The free ball potted, meanwhile, is spotted.
If no reds remain on the table, then the nominated free ball assumes the identity and value of the lowest-value ball on the table. But in this case, after such a free ball is potted, the ball on will of course be the object of the next shot. Say only the brown, blue, pink and black remain on the table. A player fouls, and the in-coming player is snookered. He nominates the blue as a free ball. If he pots it, he gets 4 points (the value of the brown), the blue is spotted, and the next shot is on the brown, for another four points.
NB: it is illegal to cause a snooker with a free ball, unless only the pink and black remain. Therefore if, in our previous example, the player with the free ball, ignorant of the rules, chose to roll the cue-ball up behind the blue, he would have fouled, and therefore been penalised by the value of the ball on (here, the value of the brown, four points). (And then the player fouled against, who is now himself snookered as a result of a foul, may nominate a free ball). This rule does not apply, however, when just the pink and the black remain on the table, for if it did, it would be impossible for the player with the free ball to lay snookers, particularly if he is lagging way behind as regards the score. If he's more than 13 points behind, the combined value of pink and black, then snookers are the only way he can win the frame.