In football move, run faster to leave United floundering (8)
I believe the answer is:
transfer
'in football move' is the definition.
'transfer' can be an answer for 'move' (transfer is a kind of move). I am unsure of the 'in football' bit.
'run faster to leave united floundering' is the wordplay.
'to leave' indicates named letters should be taken away.
'united' becomes 'u'.
'floundering' is an anagram indicator.
'run'+'faster'='runfaster'
'runfaster' with 'u' removed is 'rnfaster'.
'rnfaster' with letters rearranged gives 'TRANSFER'.
(Other definitions for transfer that I've seen before include "player's move" , "Move to another side or team" , "Give over!" , "Move something from one place to another" , "Footballer maybe" .)