Making an inferior move to get out of threefold repetition? Let's say it's the last day of a tournament and white needs to win a game in order to advance to the next stage or something like that. Unfortunately, he reaches a position where there is no way to progress without making things worse somehow, and so he begins repeating the same position.

However, he doesn't want to claim a draw since it would ruin the tournament for him. Black realizes what's going on and also refuses to claim a draw, hoping that eventually white will give in and make an inferior move in an attempt to win.

Would black's behavior be considered unsporting in such a situation? Has something like this happened in a tournament before? Could this theoretically go on forever in a game with time increment?
Could this theoretically go on forever in a game with time increment?


No, because the arbiter would step in and declare the game drawn after the fifth repetition of the position.

According to the FIDE Laws of Chess -


  9.6 If one or both of the following occur(s) then the game is drawn:
  9.6.1 the same position has appeared, as in 9.2.2 at least five times.


and -


  9.2.1 The game is drawn, upon a correct claim by a player having the move, when the same position for at least the third time (not
  necessarily by a repetition of moves):
  9.2.1.1 is about to appear, if he first writes his move, which cannot be changed, on his scoresheet and declares to the arbiter his
  intention to make this move, or
  9.2.1.2 has just appeared, and the player claiming the draw has the move.