To [email protected], that really just depends on what type of tournament or play it is. Each chess organization has its own rules about announcing things and how honest mistakes are dealt with. Generally speaking in blitz games (less than 5 minutes per side), there are some unwritten rules about how illegal moves result in a loss for that player (or it's up to the opponent whether to "forgive" the mistake).
To comment further on the casual under-5 minute games (aside from the castling question), anyone who moves without noticing he or she is in check can actually have his/her king captured/game over. The reason is because the opponent shouldn't have to be wasting his or her clock time saying "oh no you can't do that, sorry."
To [email protected], that really just depends on what type of tournament or play it is. Each chess organization has its own rules about announcing things and how honest mistakes are dealt with. Generally speaking in blitz games (less than 5 minutes per side), there are some unwritten rules about how illegal moves result in a loss for that player (or it's up to the opponent whether to "forgive" the mistake).
To comment further on the casual under-5 minute games (aside from the castling question), anyone who moves without noticing he or she is in check can actually have his/her king captured/game over. The reason is because the opponent shouldn't have to be wasting his or her clock time saying "oh no you can't do that, sorry."