I thought it was an illegal move in chess to castle through a square that is being attacked by one of my pieces??
How come my opponent just did this and cost me the game??
Black move 15 in this game....?
https://www.chess.com/live?#g=3346167489
Thanks in advance....?
The rook can go through "check"; a king can't.

To me, it seemed more like your dropping a knight was the cause of your loss.
I thought it was an illegal move in chess to castle through a square that is being attacked by one of my pieces??
How come my opponent just did this and cost me the game??
Black move 15 in this game....?
https://www.chess.com/live?#g=3346167489
Thanks in advance....?