Get beaten outside - nothing is not fixed (5)
I believe the answer is:
loose
'is not fixed' is the definition.
(I've seen this before)
'get beaten outside nothing' is the wordplay.
'get beaten' becomes 'lose' (I've seen this in another clue).
'outside' means one lot of letters goes inside another.
'nothing' becomes 'o' (O resembles 0).
'lose' going around 'o' is 'LOOSE'.
(Other definitions for loose that I've seen before include "Slack; not exact" , "Unsecured; dissolute" , "Unconfined" , "Liberal" , "Vague -- insecure" .)