United move up in lead (8)
I believe the answer is:
together
'united' is the definition.
(I've seen this in another clue)
'move up in lead' is the wordplay.
'move' becomes 'go' (to go is to move).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'in' means one lot of letters goes inside another.
'lead' becomes 'tether' (lead can mean a tether or leash).
'go' back-to-front is 'og'.
'og' inserted inside 'tether' is 'TOGETHER'.
(Other definitions for together that I've seen before include "In one another's company" , "Level-headed" , "at the same time" , "as a group" , "tied" .)