Opening Attack

An opening attack can be made on an enemies turn if they try and move out of your combat range, or if the target does anyother action which causes them to make an opening your character could take advantage of. These might include if they try to cast non combative magic within your melee weapons range, try and target another character with a ranged attack when within your melee combat range, or if they try and move outside your combat range when they were already inside it.
You and your game master might also find that other actions or choices the target makes might open them to other opening attacks to take advantage of.