Once per player per turn, when a unit's Surge is triggered, a player may choose one: Pay 1 Force to put 1 captivity counter on a unit in that arena. Or: Pay 1 Force to remove 1 captivity counter from a unit in that arena.
Keywords
Surge
Surge X: A cumulative, triggered ability that means, "Whenever another unit damages this unit, you may give a unit of your choice in this arena +X power until end of turn."