Ace learns after transfer they could face Chelsea (7)
I believe the answer is:
arsenal
'they could face chelsea' is the definition.
(Arsenal and Chelsea are footballing rivals)
'ace learns after transfer' is the wordplay.
'ace' becomes 'a' (abbreviation).
'after' is a charade indicator (letters next to each other).
'transfer' indicates an anagram (I've seen 'transferring' mean this).
'a'+'learns'='alearns'
'alearns' anagrammed gives 'ARSENAL'.
(Other definitions for arsenal that I've seen before include "Weapon store - team" , "Supply of weapons" , "Armoury - London football club" , "Store of guns and ammunition" , "Highbury football team" .)