Thinking about it further, what should the TD do if alerted to Player C's speech ~before~ Player B acts?
Allow Player A to reconsider his action? If Player B is allowed to act with the new info, shouldn't Player A have that same opportunity?
Freeze the action (and rescind Player A's river bet) and go directly to showdown? Seems less clear under these circumstances, especially since Player B hasn't even acted.
Here's another twist: what if Player B has the suited ace vs holding the king? He would be a lot more likely to call with the nut flush before or after hearing Player C's remarks. Same as if Player C remark had been "I folded the ace!" -- because holding the King, Player B now only has to worry about the SF and would be more likely to call.
Player A doesn't deserve to get shafted here because of something done beyond his control by another player. And Player B doesn't deserve to get rewarded for it, but he also doesn't deserve to get shafted if he was going to call before he heard the 'helpful' remarks.
I actually think the proper rulings are probably different depending on whether or not Player B has acted after receiving the extra information. I'm just not yet sure what those rulings should be..... although protecting Player A from unwarranted damages is as high a priority (to me, in the best interest if the game) as ensuring that the best remaining live and untainted hand wins the pot.
Disclaimer: Okay I need to put this out there, I think we can run this down a few ways that this plays out, and its more of a though experiment than discourse / argument. The following scenarios I don't think are statistically likely but should at least be considered.
I love the rewind and let player A have the option, but I would limit the options as to take it back or let it stand.
If player A had put in 1/2 a stack, does this now open player A's option to push All in? Is there a world where player A checks and player B doesn't bet, at this point player A shows any weakness it means s/he doesn't have 1 of the 2 cards that could beat player B. (do you lose player A)
IQ 1million player A takes it back and checks to player B, who goes all in, player A snap calls with the nuts. (I think you'd lose a player)
If you give player A the option, and s/he doubles down on the 'move', does that harm player B in the process? Wouldn't the reaction of player B to player C's info be a change to the information, and would that info lopsided? Am I overthinking this? (spoiler I typically do hahaha)
A bit further down the rabbit hole, does the TD's knowledge of player A's cards taint the process, does player A's cards need to remain anonymous to the TD, should it have an impact on the decisions? In BlackJack you get the option for insurance...
If player C was mistaken or lying to bait player B into calling? (sticking with something punitive for the behavior but would this info change the severity of the penalty?)
If player A and player C are not colluding and player A has the straight flush, you still can't let player B know that player C was mistaken or lying if that is the case, and opening the up the option to let player A make it look like he's bluffing even more is kinda harsh to player B.