Aggressor calculatingly holding back game (8)
I believe the answer is:
lacrosse
'game' is the definition.
(lacrosse is a kind of game)
'aggressor calculatingly holding back' is the wordplay.
'holding' indicates the answer is hidden within the clue.
'back' shows that the letters should be reversed in order.
'essorcal' is hidden within 'aggressor calculatingly'.
'essorcal' backwards is 'LACROSSE'.
(Other definitions for lacrosse that I've seen before include "Game played with netted sticks" , "Sport played with sticks" , "Ball game using netted stick" , "Game played with nets on sticks" , "Like thirteen of the other clues in the French" .)