Main event – it’s possibly holding football team back (7)
I believe the answer is:
tsunami
'main event' is the definition.
'tsunami' can be an answer for 'event' (tsunami is a kind of event). I am not certain of the 'main' bit.
'it's possibly holding football team back' is the wordplay.
'possibly' indicates an anagram.
'holding' is an insertion indicator.
'football team' becomes 'man u' (short for Manchester United).
'back' says the letters should be written backwards.
'manu' written backwards gives 'unam'.
'its' is an anagram of 'tsi'.
'tsi' placed around 'unam' is 'TSUNAMI'.
Can you help me to learn more?
(Other definitions for tsunami that I've seen before include "Destructive tidal wave" , "I am nuts! (anag)" , "crashing bore" , "wall of water" , "Seismic sea wave" .)