Imagine a situation where our queen, opponent's bishop and opponent's king are in same vertical line such that if bishop was not there, there would be a check. Now the opponent, somehow unnoticeably removes the bishop from the line which straight leads to our victory. . . So is this a fouls and should be reversed or a rule or something?? Answer please,!!!
This depends on the rules you are playing under:
In blitz chess with very short time control, an illegal move, such as putting your king into check, usually loses.
In Fide rated tournament games only the second illegal move loses, so he would just have to put the bishop back and make a different move with the bishop (such as taking your queen …).
In olden times there was the rule that you'd have to take back an illegal move and make a king move instead, as a way of punishment, because quite often making a king move would just be a loss of time. I think this is a good compromise for casual games.
I remember an anecdote about this old rule: Two masters were playing and after 2…Qd5 white wanted to attack the queen with 3.Nc3. But he fumbled the piece and played 3.Bc3 instead.
The king move punishment unfortunately led to immediate mate …
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1 1.e4 d5 2.exd5 Qd5 3.Ke2 Qe4#