You cannot prevent your enemy from doing what he wants to do, except by force of arms. Rules Activation is unit by unit. A unit can be 1 creature, hero or monster or it can be a group of models.
Units can be as large or as small as a player desires.
All actions in Battlestorm are considered simultaneous, but for the purposes of tabletop play we focus on units by separating them between activated and inactive units. To determine who is activated, both sides roll a d30. The player with the highest roll must activate one unit. An activated unit may move. An activated unit may move and fire a projectile.