Recommend that anyone that leaves or is kicked in the middle of a clan war does not receive a loot bonus. Hoppers come in and attack the highest farmer then leave and get the bonus. When the leader tells clan members to attack in their range and a hopper does this it just doesn't look right and no consequences for the hopper. This will help stop hoppers from leaving in the middle of a war and members entering clans that are ineligible for clan war.
