Back the French regular team (6)
I believe the answer is:
eleven
'team' is the definition.
(eleven is a kind of team)
'back the french regular' is the wordplay.
'back' shows that the letters should be reversed in order.
'the french' becomes 'le'.
'regular' becomes 'even' ('even' can be similar in meaning to 'regular').
'le' written backwards gives 'el'.
'el'+'even'='ELEVEN'
(Other definitions for eleven that I've seen before include "Enough for a soccer side" , "Football team; number" , "Bingo's "legs"?" , "Sporting side" , "Cricket 18" .)