Unit Group - Pick every unit in (Units within 275.00 of FragmentationShotPoint matching ((((Matching unit) is A structure) Equal to False) and ((((Matching unit) is Magic Immune) Equal to False) and ((((Matching unit) is A ground unit) Equal to True) and ((((Matching unit) is Mechanical) Equal to False) and do (Actions)
Loop - Actions
Unit - Cause FragmentationShotCaster to damage (Picked unit), dealing 100.00 damage of attack type Chaos and damage type Normal
This is what Rvituapek meant. This is taken from my own map's trigger, where FragmentationShotCaster is the casting unit of the spell and FragmentationShotPoint is the target point of ability being cast. However, you will need to specify what type of units will be affected in the trigger. For example, i dont want the spell to hit air, structures, mechanical or magic-immuned units, thus the trigger.