Ok so the revised rules:
In the first turn of combat (if two fighters are already engaged in combat and another charges into the fight the model on it's own doesn't get the shield bash attack but the model charging could) a model armed using a shield may make a shield bash attack at a man sized model not using a shield. The attack is done before the model's other attacks unless they have an allways strikes first weapon in which case they can choose to strike in normal order and bash before attacking or bash after striking with their weapon.
This attack is at +1 to hit with normal strength and armour saves as normal (-str modifiers.) A buckler can be used to parry but if a weapon or bracers are used and succesfully parry then the model counts as having rolled a 3 on the table below.
1-2 nothing happens.
3 the opponent may not counterattack as you hit his weapon (if they have an offhand weapon they may still attack with that.)
4 the opponent is knocked back d3 inches and may not counter attack, the shield basher may elect to follow up.
5 knocked down
6 stunned (helmet saves may be taken)
Shields cannot use the cutting edge special rule.
And then mabye -1 to climbing/diving ect rolls if you guys think thats needed.
