Punch yobbo roughly to start with (5)
I believe the answer is:
clout
'punch' is the definition.
(I know that punch can be written as clout)
'yobbo roughly to start with' is the wordplay.
'yobbo' becomes 'lout' (I've seen this before).
'roughly' becomes 'c' (circa).
'to start with' is a charade indicator (letters next to each other).
'lout' after 'c' is 'CLOUT'.
(Other definitions for clout that I've seen before include "Wallop - influence" , "Cuff" , "Whack" , "Box" , "A blow; powerful influence" .)