Blockade, for instance, European is backing (5)
I believe the answer is:
siege
'blockade' is the definition.
(siege is a kind of blockade)
'for instance european is backing' is the wordplay.
'for instance' becomes 'eg' ('e.g.' can be a synonym of 'for instance').
'european' becomes 'e' (abbreviation e.g. EU).
'backing' is a reversal indicator.
'eg'+'e'+'is'='egeis'
'egeis' in reverse letter order is 'SIEGE'.
(Other definitions for siege that I've seen before include "Military operation surrounding a town" , "Isolating attack" , "Military operation ringing a town" , "Military operation to seal off (town)" , "Military encirclement" .)