Question - What is Blackmail in Gaming?
Answer - Being forced into a making a move, that you wouldn't otherwise make.
Now in your typical one on one game of Chess, it's irrelevant, you both want to win, you make the optimal moves. You have to play defence as well as offence.
But in a multiplayer game say a 4 player one, everyone at the table wants to win, and has responsibility to stop others. If they choose to do nothing to help stop a certain player win they can hardly complain when another player also does nothing!
Lets have an example. Players A,B,C and D.
Player A makes a move, If no other players make a specific move to stop them they will win. Player B ignores that and advances their win, reasoning that the C or D will stop it. C ignores it too... D is now forced to stop the win or the game will end. This is blackmail in gaming.
D duly stops the win, but warns the other players if they don't help stop the win in future, then tough, they aren't going to be the fall guy over and over.
Player A makes another winning move. B ignores it, C ignores it, D has to stop it again. At this point sure, it's great for B and C they are getting closer to winning, but D is making no progress, it's not fair and if the others want to stay in the game, they will need to step up.
Player A makes another win bid. B and C both ignore it again. D says "Fine", makes a different move and A wins. Players B and C, shout at Player D. WHY DIDN'T YOU STOP IT, YOU IDIOT!
Player D at this point has had enough and isn't willing to play any more...
If any one player at the table wants to win they have to invest, they cannot expect player D to save the game over and over, just so that they can win. Why would player D do that? There gets to a point where keeping the game going is not worth the effort for player D, the other players are getting ahead, and if they refuse to help, you know they'll just end up winning instead. Being the fall guy is not fun.
Of course everyone wants to win, that is the goal of the game, but the aim of the game is to have fun. Telling a player they are an idiot for not playing the game the way you want them to is not conducive to this...