When not all waste is recycled, it's a blow (4)
I believe the answer is:
swat
'blow' is the definition.
(swat is a kind of blow)
'when not all waste is recycled it's a' is the wordplay.
'when not all waste' becomes 'sw' (I can't justify this - if you can you should believe this answer much more).
'is recycled' indicates an anagram.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
't'+'a'='ta'
'ta' anagrammed gives 'at'.
'sw'+'at'='SWAT'
Can you help me to learn more?
(Other definitions for swat that I've seen before include "Hit with a sharp blow" , "Hit (insect) sharply" , "land crushing blow" , "Hit a wasp or fly" , "District of Pakistan; sharp blow" .)