Football team with mass appeal deliver (7)
I believe the answer is:
manumit
'deliver' is the definition.
(thesaurus)
'football team with mass appeal' is the wordplay.
'football team' becomes 'manu' (short for Manchester United).
'with' means one lot of letters go next to another.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'appeal' becomes 'it'.
'manu'+'m'+'it'='MANUMIT'
(Other definitions for manumit that I've seen before include "release" , "Set free from slavery - anti-mum (anag)" , "deliver" .)