Arrested by cop, charged journalist had a swagger (7)
I believe the answer is:
pranced
'had a swagger' is the definition.
(prance can mean to move with swaggering movements)
'arrested by cop charged journalist' is the wordplay.
'arrested by' is an insertion indicator.
'cop' becomes 'pc'.
'charged' becomes 'ran'.
'journalist' becomes 'ed' (short for editor).
'pc' enclosing 'ran' is 'pranc'.
'pranc'+'ed'='PRANCED'
(Other definitions for pranced that I've seen before include "How one of Santa's team moved" , "with springing steps?" , "moved ostentatiously" .)