It's vital to keep team winning (13)
I believe the answer is:
prepossessing
'winning' is the definition.
(I've seen this before)
'it's vital to keep team' is the wordplay.
'it's vital' becomes 'pressing' (both can mean urgent).
'to keep' means one lot of letters goes inside another.
'team' becomes 'posse' (I have seen 'legal team' mean 'posse' so perhaps 'team' could also mean 'posse').
'pressing' enclosing 'posse' is 'PREPOSSESSING'.
(Other definitions for prepossessing that I've seen before include "Attractive" , "winning" , "Fetching" , "looking good" .)