Nonsense! Walk after it when I leave (7)
I believe the answer is:
twaddle
'nonsense' is the definition.
(informal term for nonsense or rubbish)
'walk after it when i leave' is the wordplay.
I cannot really understand how this works, but
'walk' could be 'waddle' (waddling is a kind of walking) and 'waddle' is found in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for twaddle that I've seen before include "Foolish speech/writing" , "bunk" , "Pretentious or silly talk" , "Claptrap" , "Trivial speech or writing" .)