Legal ambiguity (8)
I believe the answer is:
loophole
'legal ambiguity' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for loophole that I've seen before include "Means of evasion" , "Opportunity to evade difficulty" , "Flaw in the law?" , "Ambiguity allowing one party to escape contract" , "Ambiguity (in rules) through which one can avoid punishment" .)