Lifting cap, one means to punch peace-lovers (9)
I believe the answer is:
pacifists
'peace-lovers' is the definition.
(pacifists support peace)
'lifting cap one means to punch' is the wordplay.
'lifting' says the letters should be written backwards.
'one' becomes 'i' (Roman numeral).
'means to punch' becomes 'fists' (fists can be used to punch).
'cap' in reverse letter order is 'pac'.
'pac'+'i'+'fists'='PACIFISTS'
(Other definitions for pacifists that I've seen before include "People refusing to fight" , "Those who reject war as an instrument of policy" , "they won't fight" , "They don't believe in fighting" .)