In the event I exercised a certain restraint (3)
I believe the answer is:
tie
'restraint' is the definition.
(I've seen this before)
'in the event i exercised a certain' is the wordplay.
'in' indicates a hidden word.
'TIE' can be found hidden inside 'event i exercised certain'.
(Other definitions for tie that I've seen before include "Dead-heat" , "Bond; draw" , "garb" , "Bind; be equal" , "Draw - knot" .)