Doncaster's top team is included but broken up (9)
I believe the answer is:
disunited
'broken up' is the definition.
(disuniting is a kind of breaking up)
'doncaster's top team is included' is the wordplay.
'top' says to take the initial letters (in a down clue, the first letter is top).
'team' becomes 'united' (eg Manchester United football club).
'included' is an insertion indicator.
The first letter of 'doncaster' is 'd'.
'd'+'united'='dunited'
'dunited' going around 'is' is 'DISUNITED'.
'but' acts as a link.
(Another definition for disunited that I've seen is " Split".)