Nab everyone, not hard to say boo (7)
I believe the answer is:
catcall
'boo' is the definition.
(I've seen this before)
'nab everyone not hard' is the wordplay.
'nab' becomes 'catch' (I've seen this in another clue).
'everyone' becomes 'all' (all people).
'not' suggests deleting specific letters.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'catch'+'all'='catchall'
'catchall' with 'h' taken out is 'CATCALL'.
'to say' is the link.
(Other definitions for catcall that I've seen before include "Derisive call" , "Boo" , "Jeer" , "Express disapproval" , "Mocking remark" .)