Team lost a friend (4)
I believe the answer is:
mate
'a friend' is the definition.
(I know that mate is a type of friend)
'team lost' is the wordplay.
'lost' is an anagram indicator.
'team' with letters rearranged gives 'MATE'.
(Other definitions for mate that I've seen before include "One of a pair or a pal" , "Freind, companion" , "Finish game" , "Chess finale" , "tea" .)