United's defensive blunder in tie (8)
I believe the answer is:
together
'united's' is the definition.
(thesaurus)
'defensive blunder in tie' is the wordplay.
'defensive blunder' becomes 'og' (own goal, football blunder).
'in' means one lot of letters goes inside another.
'tie' becomes 'tether' (I've seen this before).
'og' going within 'tether' is 'TOGETHER'.
(Other definitions for together that I've seen before include "Jointly" , "in league" , "In each other's company" , "Collected" , "stable" .)