Hit with tear gas from behind, quietly scarper (6)
I believe the answer is:
decamp
'hit with tear gas' is the definition.
I can't tell whether this defines the answer.
'from behind quietly scarper' is the wordplay.
'from behind' says the letters should be written backwards (the answer has been seized by the clue).
'quietly' becomes 'p' (p for piano and quiet).
'scarper' becomes 'maced' (I am not sure about this - if you are sure you should believe this answer much more).
'p'+'maced'='pmaced'
'pmaced' backwards is 'DECAMP'.
Can you help me to learn more?
(Other definitions for decamp that I've seen before include "Move on" , "Fold tents and go" , "Split" , "Depart suddenly or secretly" , "Leave suddenly" .)