Balance concerned with team welcoming United (7)
I believe the answer is:
residue
'balance' is the definition.
(thesaurus)
'concerned with team welcoming united' is the wordplay.
'concerned with' becomes 're'.
'team' becomes 'side' (I've seen this before).
'welcoming' indicates putting letters inside (in sense of 'inviting in').
'united' becomes 'u'.
'side' placed around 'u' is 'sidue'.
're'+'sidue'='RESIDUE'
(Other definitions for residue that I've seen before include "Something left over" , "What is left over, remainder (7)" , "Part remaining" , "Small amount remaining" , "rest" .)