Consider this (illegal) position.
[FEN "5n1k/3p1p1p/3PpPpP/4P1P1/1p1p4/pPpPp3/P1P1P3/K1N5 w - - 0 1"]
If we do not consider the position's illegality, and the fact that it is clearly unwinnable by eiter player (and therefore an automatic draw even if either of the players resgined, ran out of time, etc), then this position has an interesting property. Regardless of what move every player does (which is obvious in this case, since there is always only one legal move), the position results in forced threefold repetition in 4 moves.
Now here arises a question, basically a problem creation: Which legal position has the least amount of moves to make threefold repetition, assuming no player wants to repeat the positions?