1♣ was 16-18 or 22+, any shape.
Result: 5♥X(W)=, NS-850 and 93 X-IMPs.
South reserved his rights because of what he thought was a slow pass by East over 4♠. West claimed not to have noticed any hesitation. The director was not called because he was sitting North and so was present at the table anyway. (There was no other director available to call.) In North's opinion the STOP card was (of course) used correctly, and East did not take significantly longer than the time the card was on the table, but the problem is that over 90% of club players take no notice of the STOP requirements. They tend to flash STOP card briefly when using themselves and return it straight to the box, and don't wait 6-10 seconds after their opponent uses it. If West is one such player, the pause over 4♠ conveys UI to her partner. Although all the players know each other well and play against each other every week, it's difficult for the TD to judge whether this East always pauses or never pauses (unless they need thinking time), or only pauses when playing against the director (there are some players in this category).
West was never asked why she bid 5♣, but South pointed out that it was odd that she chose to introduce her club suit at the point rather than earlier in the auction.
Any idea how to sort this sort of thing out, generally? How would you tend to rule if you established that there was a hesitation?