Back sore at first, one crying (7)
I believe the answer is:
sweeper
'back' is the definition.
(football term)
'sore at first one crying' is the wordplay.
'at first' says to take the initial letters.
'one crying' becomes 'weeper' (I've seen this in another clue).
The first letter of 'sore' is 's'.
's'+'weeper'='SWEEPER'
(Other definitions for sweeper that I've seen before include "'Football defender, carries a brush (7)'" , "cleaner" , "Last football defender before the goalkeeper" , "Defensive footballer" , "Soccer defender" .)