10 Giving check
You have to react to a check because the king must not be taken. There are three possible ways to get out of check:
- move the king away
- take the piece which is giving check
- move one of your own pieces to block the check (not possible when the check is by a knight)
If one side keeps on giving check and the other side's king cannot escape the checks, we call that perpetual check. Perpetual check is a good defebsive option if you are in a bad position and want to force a draw. If a position is repeated three times the game is drawn.