Ran round Sidney, off-balance (8)
I believe the answer is:
lopsided
'off-balance' is the definition.
(thesaurus)
'ran round sidney' is the wordplay.
'ran' becomes 'loped' (loping is a kind of running).
'round' is an insertion indicator.
'sidney' becomes 'Sid' (Sid is short for Sidney).
'loped' going around 'sid' is 'LOPSIDED'.
(Other definitions for lopsided that I've seen before include "Unbalanced" , "Askew, awry" , "Off balance" , "Not symmetrical" , "Askew, wonky" .)