“He’s no team player!” Aunt is livid I’d fouled up (13)
I believe the answer is:
individualist
'he's no team player' is the definition.
(someone working for themselves, not a team)
'aunt is livid i'd fouled up' is the wordplay.
'fouled up' is an anagram indicator.
'aunt'+'is'+'livid'+'id'='auntislividid'
'auntislividid' anagrammed gives 'INDIVIDUALIST'.
(Other definitions for individualist that I've seen before include "One with an independent outlook" , "Self-centred person" , "Maverick" , "One showing independence" .)