You have several questions so I will copy and paste then answer each.
Iranu wrote:Acesinc, so when commentators say "he's nominated green as an extra yellow" for example, that's not strictly true?...
As you may know, I don't get much opportunity to watch a lot of Snooker here in USA (except the WC....I can usually make time for that and dicey internet streams seem to appear to make viewing possible; just need to be sure to keep anti-virus up-to-date
) so I think I need to guess about this question. I believe it means exactly what it appears to mean...that is, the striker's ball on is Yellow. However, due to this special rule, striker is not required to contact Yellow but will choose instead to pot a Free Ball thereby raising his score with the extra points equivalent to that of a Yellow...in effect, an "extra Yellow".
Edit: I just re-read your question after my post and now I think I better understand what you meant by it. You are correct in that the "extra Yellow" DOES NOT mean the striker can play his stroke as if there are TWO Yellows on the table and it doesn't matter which he strikes first. No, the Rule is very clear, the Free Ball MUST be the first ball contacted.
Iranu wrote:...Does this also apply to reds?...
One of the nice features about the Rules of Snooker are that there are very few "exception" rules. If a rule applies in one case, it is (almost) certain to apply in all cases. So, yes, the Free Ball rule is the same for Reds, the nominated "Free Ball" colour MUST be the first ball struck. To be perfectly (and probably unnecessarily) accurate, it would also be a legal stroke if the nominated Free Ball is the first ball contacted SIMULTANEOUSLY with the natural Ball On (whether for Colours or Reds). That is rather a non-issue however as the likelihood of a simultaneous hit occurring is about the same as a whelk's chance in a supernova.
Now that I have put my foot in my mouth about "exception" rules, I would be remiss if I did not point out that Free Ball is one of the the Rules that DOES in fact contain an exception and it is one about which few players seem aware. Most understand that (in general) it is a foul to lay a snooker on your opponent behind a nominated Free Ball whether by accident or intent. The EXCEPTION to that rule is that in the case that Pink and Black are the ONLY object balls remaining and a Free Ball is awarded (Pink is snookered behind Black), then the Black may be nominated and contacted, leaving the incoming striker snookered behind the Free Ball Black (Section 3., Rule 12. (b)(ii)). If you ever do this to someone, you are almost certain to cause an argument. I didn't; instead of arguing back with my opponent, I sought out the Tournament Director and he schooled my opponent about the Rule.
Iranu wrote:...Out of interest would it be a foul if the green was hit first but both green and yellow were potted?
No, but it is curious that you ask this precise question because I believe that THIS is exactly why our friend Finoeire posted his query in the first place. Imagine we are spectators for his match...(cue wavy lines for flashback scene)...
In the course of the frame, the Yellow and Green have made their way near a corner pocket, Yellow in the jaws and Green very close on one side. At the other end of the table, Finoeire pots the last Red and decides there is no good Colour to pot in this case. Instead he selects an arbitrary colour and simply lays a snooker on his opponent easily behind Green a very long distance away at the far end of the table. His opponent heroically attempts an escape to no avail. Finoeire is Snookered after a Foul since the Yellow is "half covered by the Green". If Finoeire plays at the Yellow, he is concerned that he may clip the edge of the Green first which would be a foul. So instead he nominates the Green as Free Ball but sadly, he does not understand the Free Ball rule very well at this time. Finoeire tries to just barely graze the edge of the Green and strike Yellow for the pot afterward and in so doing, misses Green completely instead striking Yellow ball first. Foul, four away to his opponent as described.
(cue wavy lines and back to Reality...)
Had Finoeire been familiar with the Rule prior to the stroke, he would have known to play his stroke this way instead...nominate Green as Free Ball. Simply and gently plant the Green onto Yellow potting Yellow in the process for two points. Yellow ball had been legally potted
, therefore it remains in the pocket and Green is now the Ball On and an easy pot since it is now sitting in place of Yellow in the jaws of the pocket. Finoeire may also have had a fear that had he tried this, Green may also have fallen in the pocket behind Yellow and perhaps he feared this would have been a foul stroke. Again, had he been familiar with the Rule prior to the stroke, he could have played confidently because even if the Green followed Yellow into the pocket, it is NOT a foul stroke. Perfectly legal to pot a Free Ball and also the natural Ball On in the same stroke. (You have probably seen this happen before with Reds when a Free Ball colour is potted and another Red flukes into a pocket as well. Perfectly legal.) If that Green HAD followed Yellow into the pocket, it would have been perfectly legal, but the Green would then be re-spotted and would become the Ball On for the next stroke.