What would you do if, at the start of a frame...

[Souwester]

What would you do, if at the start of a frame, you, as referee, have inadvertently placed the yellow on the green spot and the green on the yellow spot? Player A who broke notices it at the completion of his break off stroke.

[jrc750]

I would swop the balls to the correct positions, and to avoid any possible ill feeling offer the player the option to break again
Edit: Is it fair to call a foul ? not really the players job to check the ref has done his job properly !

[vucko117]

Call a foul and leave the balls where they are (Player B has the usual options after a foul)

I think this is the best option I would be a very cruel referee

[The Statman]

I think you would either have to allow the frame to continue, or reset the balls and have the player break off again.

I did once referee a game where this had happened - but it wasn't noticed until the player potted the green off the first red. The green spot was of course occupied by the yellow and the player wasn't best please for it to go on the black spot, tying up the black!

[best1966]

Well you can't call a foul as it's a referees mistake. But i'm pretty sure that providing player B hasn't played a shot yet, you can swap the balls over. If the mistake isn't noticed until both players have played a stroke, then both balls remain where they are.

[Souwester]

Ok, to answer the question. First, a player can't be held responsible for a mistake of the referee in spotting colours. If a stroke is played with a ball or balls incorrectly spotted, they will be considered to be correctly spotted for subsequent strokes, without penalty.

The correct answer in the poll is, therefore, the final one: no foul and let player B play from where the position left.

7. Spotting Colours
Any colour pocketed or forced off the table shall be spotted before the next stroke is made, until finally potted under Section 3 Rule 3(f).

(a) A player shall not be held responsible for any mistake by the referee in failing to spot correctly any ball.

(b) If a colour is spotted in error after being potted in ascending order as per Section 3 Rule 3(f)(iii), it shall be removed from the table without penalty when the error is discovered and play shall continue.

(c) If a stroke is made with a ball or balls not correctly spotted, they will be considered to be correctly spotted for subsequent strokes. Any colour incorrectly missing from the table will be spotted:
(i) without penalty when discovered if missing due to previous oversight,
(ii) subject to penalty if the striker player before the referee was able to effect the spotting.