Strike many as being in the bag (5)
I believe the answer is:
smack
'strike' is the definition.
(thesaurus)
'being in the bag' is the wordplay.
'being' becomes 'm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in the' is an insertion indicator.
'bag' becomes 'sack' (sack is a kind of bag).
'm' going inside 'sack' is 'SMACK'.
'many as' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for smack that I've seen before include "Hit - drug" , "Sharp taste" , "Distinctive trace" , "Kiss - fishing vessel - taste - heroin" , "Loud kiss" .)