Football team, English, left day before November (6)
I believe the answer is:
eleven
'football team' is the definition.
(synonyms)
'english left day before november' is the wordplay.
'english' becomes 'E' (abbreviation).
'left' becomes 'l' (common abbreviation).
'day before' becomes 'eve' (the eve of something is the night before).
'november' becomes 'N' (phonetic alphabet: alpha, bravo, charlie etc.).
'e'+'l'+'eve'+'n'='ELEVEN'
(Other definitions for eleven that I've seen before include "Odd number for a team" , "Number, on a team perhaps" , "Lowest two-digit prime" , "sports team?" , "Football or cricket team?" .)