Andre147 wrote:chengdufan wrote:Thanks HappyCamper

So a particular non-sporting sort, let's call him Player B, could in theory do the following.
Player A needs a red and a black to get to the snookers required stage. He pots the red, and the white is headed nicely towards perfect position on the black.
Player B, walking with a resigned look back to his chair, let's his cue 'slip' and hit the green.
Foul and 4 away, but not the 7 needed. And now player A finds himself with no pot available for the next ball on, the yellow.

In that instance the referee will warn the offending player for unsporting conduct, and were he do make another similar action again he would forfeit the frame.
Andre, of course I have the greatest respect for your knowledge and experience, but I don't think you have the complete story for this one. I admit that I cannot find a specific Rule to cover this exact circumstance, but navigating around the Rules with my magnifying glass and Holmesian cap and overcoat, my own ruling appears to differ from yours. I invite response and will be happy to be corrected if necessary.
Start with Section 2., Definitions, 15. Infringements, Fouls and Penalties:
"An infringement is any violation of these Rules.
A foul is an infringement which will end the offender’s turn.
Penalties are infringements which do not affect the order of play."
So what we actually have here is an infringement, not a foul. It will have no effect on the order of play, meaning that the infringement causes additional penalty points to be awarded above and beyond the points scored in the striker's turn at the table. So the non-striker commits an infringement, the Referee calls, "Foul," (or maybe he or she says, "Penalty!" instead....I have never been certain about this one,) appropriate points are awarded, and the striker simply continues his turn at the table, playing at the colour of his choice.
EDIT: I literally just learned something re-reading what I wrote above! The Referee WILL call, "Penalty!" and not "Foul!". All Penalties and Fouls are considered to be infringements, but a Penalty is not the same thing as a Foul, and a Foul is not the same thing as a Penalty (although "penalty points" are awarded for ANY infringement). In other words, a PENALTY is essentially a foul which is committed by the NON-striker (so you don't call it a "foul", get it?) No wonder I have been confused about this for so long! END EDIT
Moving on to Section 3., Rule 10. (i):
"If a striker fouls any ball including the cue-ball prior to striking it, the appropriate penalty will be imposed. The non-offender may then elect to play themselves from the position left, or request the offender to play again from the position left or the original position. In the latter case, all balls shall be replaced and the ball on shall be the same as it was prior to the infringement, namely:
(i) any Red, where Red was the ball on;
(ii) the colour on, where all the Reds were off the
table;
(iii) a colour of the striker’s choice, where the ball on
was a colour after a Red, or a free ball nominated
as a Red had been potted.
A consultation period starts when the request is made
to replace the ball(s)."
While this Rule is written in regards to the striker, I assume the same would apply in the case of an infringement by the non-striker implying that the next ball on will be a colour of the striker's choice, certainly not the Yellow ball unless that is the choice. So Player A may still play at the Black if he wishes, then followed by Yellow for the final sequence. In fact, the implication of this Rule is that the striker may now choose to have the Green replaced to where it had been or leave it in its new position if that is beneficial to him. I am not certain of this; merely trying to interpret what is written.
In fact, the assumption thus far has been that the penalty given for the now properly termed infringement would be four points as it was the Green that was disrupted. I believe the argument can actually be made that the penalty in fact should properly be seven. It would depend on whether the Referee had determined if the previous stroke of potting the Red had truly been completed. It is not a simple matter of "did the balls all stop moving?" If the White is moving in the direction of a pocket and there is even a small chance that it may go in off for a foul, then the Red stroke is certainly not complete. But the original description states, "...white is headed nicely towards perfect position on the black." With that, the Referee may have legitimately determined that the Red stroke is complete. You may notice on occasion that a Referee may call out the score, "One!" while there may still be some residual motion in the White or other balls, but clearly no further consequential actions will occur before the next stroke. So as our theoretical White was moving to perfect position on Black and the infringement occurred, the Referee may have already self determined the Red stroke as being complete and that we are now in a state of undetermined Colour. (He would NOT assume the ball on to be Black.....perhaps White may end up stopped with Pink in better position? The Referee will make no assumption here until he determines a nomination from the striker). In a state of as yet undetermined choice of colour, penalty points awarded will always be seven. So I believe the value of this penalty would be at the discretion of the controlling Referee, maybe he would call it four, maybe he would call it seven.
After all that, I certainly agree with Andre's assessment that a stern warning is in order. However, Player B undoubtedly will NOT benefit from his nefarious scheme. Quite the contrary, he has now found himself deeper in the hole, and with a recorded warning of unfair play and poor conduct. Crime does not pay.
Feel free to add, subtract, comment, correct.