Missile Weapons and Melee Combat
This rule change is an interesting addition, proposed by one of the players. It has been modified only slightly.
When firing a missile weapon into combat, that attack role usually incurs an extra -4 as a circumstance modifier because the target is moving in response to attacks from others in adjacent squares.
This modifier will continue to apply, but if the -4 is what causes the attacker to miss their opponent (i.e. the dice roll plus all modifiers would normally have hit, but the application of the extra -4 causes the shot to miss) then the attacker must select one of the other participants in the original target's melee at random (both friend and foe included - as long as they are adjacent to the original target, or have reach weapons that bear) and make a new attack roll against them. This second roll is adjusted with the same modifiers as the original roll, except that the -4 'firing into melee' combat modifier does not apply.
If the attack hits, then calculate damage in the normal way. Any extra effects or spells wrapped into the attack are also applied, or any extra damage types that were part of the original attack are also carried in. If the damage could be factored in a choice of ways, then the choice must be made as though the original target was being hit.
The effect here is that firing into melee combat is not a safe option, there is a chance (albeit a slim chance with well-armoured friends) that you could hit a friendly target. And in trying to do your best, you may find that back-stab bonuses and/or critical hit bonuses also apply.
There are feats available that can negate the penalty for firing into combat. If the penalty is avoided, then this rule does not apply.