If you've played Clash of Clans for more than a week you know that every player now has two different bases: the regular base and the war base. You also have two castles: the war castle for defense in clan wars and the clan castle for everything else. There is a wiki with more clan war basics. You should definitely read it if you haven't yet. Want more? Read this excellent clan war advice on Reddit.
The war castle is your best and strongest defense in clan wars.* Let's say your war castle holds 20 troop units and your clan mates fill it with level 5 wizards. They can do a total damage per second of 170*5 = 850 dps (splash ground and air) to attacking troops!
Because a war castle full of wiz can fry 30 hogs faster than you can say "wizard bacon" the first thing a decent attacker will do is use giants, wall breakers or hogs to try to lure your war castle troops out and kill them before starting the rest of the attack. Don't let them kill your castle troops!
