can some one explain what a ninja is and some examples please thanks.

we are not talking about those men dressed in black!

A ninja is basically when the defending playing in an attack either: builds enough fleet/defense that they won't lose the attack; or: they have their fleet land just before the attacking one so they also win.

Oh, I remembered a third one: They move their fleet and/or res just before the hit lands so the attacker doesn't get anything.

I know there are more ways, I just can't remember them right now.