With assistance, I surpass obstacle (8)
I believe the answer is:
handicap
'obstacle' is the definition.
(I've seen this before)
'with assistance i surpass' is the wordplay.
'with' is a charade indicator (letters next to each other).
'assistance' becomes 'hand' (hand is a kind of assistance).
'surpass' becomes 'cap' (I've seen this before).
'hand' next to 'i' is 'handi'.
'handi'+'cap'='HANDICAP'
(Other definitions for handicap that I've seen before include "Disadvantage imposed on competitor to equalise chances" , "Impediment, hindrance" , "golfer's measure of skill" , "Hold back" , "Impede" .)