Escape clause (8)
I believe the answer is:
loophole
'escape clause' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for loophole that I've seen before include "useful for defence" , "Ambiguity that makes it possible to evade an obligation" , "Flaw or ambiguity in a rule" , "escape mechanism" , "way to escape penalty" .)