[patroclo]

Don't know if it's been signaled.
I think that should be useful to know what opponent refuse claim
Gigi

[inquiry]

Who rejected the claim is not signalled, and in fact, you can reject your own claim, and that isn't signalled either (maybe claim cancelled instead of rejected might be good wording).

Sadly, the quality of bridge is all to often so low that good claims are rejected. In the real world, when a claim is made, all play stops, and the validity of the claim adjudicated. With online bridge, sadly, play must proceed if it is rejected.

I wonder why you feel it would be "useful" to know who rejected the claim. Of course, if a defender claims, he knows it was declarer who rejected the claim. Are you just curious as to who doesn't understand bridge, or do you think such knowledge might be useful in finishing playing the hand? If declarer makes a claim that is rejected, then knowing which opponent rejected it might help with his subsequent line of play (if such knowledge was helpful) maybe by figuring out a suit is splitting badly? This really should be the point, for one thing, both opponents can see all the cards when you claim, so either one might be rejecting based upon cards in their partner's hands. Second, I would never take advantage of a rejected claim to change my proposed line of play (presumably the claim included some line of play).

[flytoox]

Hehe, I once met an cunning guy. We bid 6M and he dbled. It is cold, after a few rounds card played, my pd claimed mk. But this guy rejected, then he claimed down 1. MY pd thought this guy claimed make and accepted. Then he asked me, why it is down one? Hehe.

[Gerben47]

As defender, when declarer makes an incorrect claim, I don't play on but since I can look at all 52 cards now I make a new offer. This way you avoid declarer taking advantage of changing his line. If I ever make an incorrect claim I hope my opponents will do the same.

Another point here: Don't claim unless you are AT LEAST 100% sure of the final result. In real life you can easily make a conditional claim (making, or +1 if the heart finesse works), but on BBO that's not so easy.

If there is a correct claim, it is the job of the claimer to EXPLAIN the claim. That's why so many good claims are rejected in my opinion, because the claimer does not take the effort to write down the intended line.