Oh no ducks, I nearly forgot! (4)
I believe the answer is:
oops
'oh no' is the definition.
I can't tell whether this defines the answer.
'ducks i nearly forgot' is the wordplay.
'ducks' becomes 'OO' (two O's - duck means zero in cricket).
'i nearly forgot' becomes 'PS' (as in a PS in a letter).
'oo'+'ps'='OOPS'
Can you help me to learn more?
(Other definitions for oops that I've seen before include "Harem" , "I've messed up" , "Blunder explanation" , "Exclamation on making minor error" , "Oh dear, I've spilt something!" .)