Coach briefly played with Leeds United (9)
I believe the answer is:
coalesced
'united' is the definition.
(coalescing is a kind of uniting)
'coach briefly played with leeds' is the wordplay.
'briefly' means to remove the last letter.
'played with' is an anagram indicator.
'coach' with its last letter taken off is 'coac'.
'coac' mixed up with 'leeds' makes 'COALESCED'.
(Other definitions for coalesced that I've seen before include "Mixed" , "Came together as one" .)