One working in lobby with assistance gets the advantage (4,4)
I believe the answer is:
whip hand
'the advantage' is the definition.
(whip hand is a kind of advantage)
'one working in lobby with assistance' is the wordplay.
'one working in lobby' becomes 'whip' (I am not sure about this - if you are sure you should believe this answer much more).
'with' is a charade indicator (letters next to each other).
'assistance' becomes 'hand' (hand is a kind of assistance).
'whip'+'hand'='WHIP-HAND'
'gets' is the link.
Can you help me to learn more?
(Other definitions for whip hand that I've seen before include "Position of power" , "powerful position" , "Advantage, dominance" , "Controlling position (held by jockey?)" , "Dominating position" .)