OnDamage does return the source of damage, s. Norbyte's list Baardvark linked above (same in D:OS 1):
OnDamage(DAMAGE:type, FLOAT:percentage, CHARACTER:source, ITEM:source)
Thrown when the object receives damage
You just have to add the OnDamage EVENT to the target's script (e. g. the 'Base' script if this shall apply to all characters in game) and let the character apply the status on himself if the source is a player (or any condition you like).