Before writing a dodgy excuse (7)
I believe the answer is:
pretext
'a dodgy excuse' is the definition.
'pretext' can be an answer for 'excuse' (a pretext is an excuse or pretence). I'm not sure about the 'a dodgy' bit.
'before writing' is the wordplay.
'before' becomes 'pre' (prefix meaning 'before').
'writing' becomes 'text' (text is a kind of writing).
'pre'+'text'='PRETEXT'
Can you help me to learn more?
(Other definitions for pretext that I've seen before include "Ostensible justification" , "Insincere excuse" , "Fictitious excuse" , "False excuse" , "Reason put forward to conceal the true one" .)