Sec. 3 Rule 12. After a foul, if the cue-ball is snookered, the referee shall state FREE BALL.
Sec. 2 Rule 17. The cue-ball is said to be snookered when a direct stroke in a straight line to every ball on is wholly or partially obstructed by a ball or balls not on. If one or more balls on can be struck at both extreme edges free of obstruction by any ball not on, the cue-ball is not snookered.
In judging whether the extreme edges of a ball may be struck by the cue ball it is important to consider the distance between the two. If the cue ball is some distance away from the object ball, then the extreme edges of the balls are at 9 o’clock on the cue ball and 3 o’clock on the red ball (blue path) or at 3 o’clock on the cue ball and 9 o’clock on the red ball (green path). This means that after a foul, any obstructing ball or balls not on must not be closer than a ball’s width, plus a very slight distance more, away from the ball on (Fig. 1) and if they are closer, then a Free Ball must be awarded. It must also be taken into consideration that a simultaneous strike of a ball on and a ball not on is a foul and is the reason for the slight extra clearance being needed as described.
This is not the case if the cue ball and the ball on are in close proximity (Fig.2) here it can be seen that the furthest point of contact on each extreme edge of the red ball is at 7 o’clock and 5 o’clock relative to the cue ball and on the cue ball they are at 11 o’clock and 1 o’clock relative to the red. Any attempt to strike the red further around its perimeter from these points with the cue ball would see it miss altogether. This means that balls not on can be a lot closer to the ball on without the referee having to consider a Free Ball after a foul. The balls not on can even be touching the ball on (Fig 3) with the same criteria driving the decision.
Referees must have this in mind, especially if the cue ball is in hand, as the rule states that a ball on must be able to be struck at both extreme edges in a straight line free from obstruction from anywhere within or on the lines of the ‘D’. All possibilities must therefore be examined, even those from positions close to but not touching any ball on that is within, or is outside but close to the ‘D’, before awarding a Free Ball.
This is also very different from the judgment that must be made after any failed attempt to strike a ball on has twice been called a Miss. If full central ball contact is available, which means the contact point of the cue ball at 12 o’clock being able to contact any ball on at 6 o’clock relative to each other in a direct line, then a warning must be given by the referee and the frame awarded if a third Miss is then the result, regardless of the scores.
If that point of contact in a direct line is not available, then as many subsequent Miss’s, deemed to be so by the referee, may be called until penalty points are required to win the frame by both or either of the players, either before or because of any foul stroke, without a warning or a forfeit.
Full Central Ball Contact is available in this example (Fig. 4) and the warning after two and forfeit after three calls of a Miss are valid. Both extreme edges are not available here unlike Figs. 1, 2 and 3 where they are, but have no relevance in such a case.