Eccentric not on strike (7)
I believe the answer is:
offbeat
'eccentric' is the definition.
(offbeat means eccentric or unexpected)
'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 "Unusual, not ordinary - or rhythmic" , "Strikingly unconventional" , "Strange" , "Unconventional or lacking rhythm" , "Unusual or unconventional - perhaps in music" .)