Nonsense about United's humiliating defeat (4)
I believe the answer is:
rout
'humiliating defeat' is the definition.
'rout' can be an answer for 'defeat' (rout is a kind of defeat). I'm unsure of the 'humiliating' bit.
'nonsense about united's' is the wordplay.
'nonsense' becomes 'rot' (rot can mean nonsense or rubbish).
'about' is an insertion indicator.
'united' becomes 'U' (abbreviation as in Man U for Manchester United).
'rot' going around 'u' is 'ROUT'.
Can you help me to learn more?
(Other definitions for rout that I've seen before include "Send fleeing" , "Big defeat" , "Easy victory (or defeat)" , "clobber" , "Trounce" .)