Start to sketch possibly libellous poster, no hurry (6)
I believe the answer is:
stroll
'no hurry' is the definition.
(to stroll is to walk casually)
'start to sketch possibly libellous poster' is the wordplay.
'start to' says to take the initial letters.
'possibly libellous poster' becomes 'troll' (someone posting abuse or libel online).
The initial letter of 'sketch' is 's'.
's'+'troll'='STROLL'
(Other definitions for stroll that I've seen before include "A casual or lazy walk" , "A quiet, pleasant walk" , "A pleasant and leisurely walk" , "Walk casually" , "swan" .)