Posted 2013-February-13, 14:31
0. What's the experience level of the individual players? Are they novices or have the been around the track a few times? Are they of sufficient calibre such that they'd be expected to have rough idea of what UI is?
1. Somethings fishy with the diagram. YOu have both S and W holding the 9♠.
2. A slow 4NT would tend to suggest IMO, that S isn't sure wether it's blackwood or not. I think N, by bidding 5♣, does the ethical thing, after perhaps spending some time thinking about his obligations. Given that 3N was offered, presumably to play opposite no extras, then a pass of 4N is sort of double shotty - it works whenever slam doesn't make (or the field doesn't bid it), or when 4N really was to play.
3. I think pass is ok. Since S presumably meant 4N to play (Side note: Seriously? With a non running suit a VERY questionable single entry?), 5♣ is a signal that the auction has gone off the rails, and at this point he's allowed to wake up at look at the contents of his hand and pass.
So, to sum up, I see no reason to make a ruling on this hand.