Team not entirely fluid in possession of ball (6,6)
I believe the answer is:
leyton orient
'team' is the definition.
(football team)
'not entirely fluid in possession of ball' is the wordplay.
'fluid' indicates an anagram.
'in possession of' means one lot of letters goes inside another (has inside).
'ball' becomes 'o' (letter resembling a ball).
'not'+'entirely'='notentirely'
'notentirely' is an anagram of 'leytnorient'.
'leytnorient' enclosing 'o' is 'LEYTON ORIENT'.
(Other definitions for leyton orient that I've seen before include "London football club" , "Footballers" .)