Pull back before beginning to fall into abyss (4)
I believe the answer is:
gulf
'abyss' is the definition.
(I've seen this before)
'pull back before beginning to fall' is the wordplay.
'pull' becomes 'lug' (I've seen this before**).
'back' says the letters should be written in reverse.
'before' is a charade indicator (letters next to each other).
'beginning to' says to take the initial letters.
The initial letter of 'fall' is 'f'.
'lug' in reverse letter order is 'gul'.
'gul'+'f'='GULF'
'into' is the link.
(Other definitions for gulf that I've seen before include "Unbridgeable disparity" , "Deep wide chasm" , "Deep inlet of sea; chasm" , "Large inlet of the sea" , "Wide separation" .)