Knight caught by misplaced big blow is staggering (8)
I believe the answer is:
wobbling
'is staggering' is the definition.
(thesaurus)
'knight caught by misplaced big blow' is the subsidiary indication.
'knight' becomes 'n' (chess).
'caught by' is an insertion indicator.
'misplaced' is an anagram indicator.
'big'+'blow'='bigblow'
'bigblow' anagrammed gives 'wobblig'.
'n' placed into 'wobblig' is 'wobbling'.
(Other definitions for wobbling that I've seen before include "Quivering" , "Unsteady; trembling" , "Unstable" .)