Unusual, not on strike (7)
I believe the answer is:
offbeat
'unusual' is the definition.
(offbeat means unusual or whacky)
'not on strike' is the wordplay.
'not on' becomes 'off' ('off' is the opposite to 'on').
'strike' becomes 'beat' (I've seen this before).
'off'+'beat'='OFFBEAT'
(Other definitions for offbeat that I've seen before include "Way-out" , "Bohemian" , "Weird - irregular" , "Strikingly unconventional" , "rather unorthodox" .)