Online commentary stream (Harsha’s first in March) (6)
I believe the answer is:
thread
'online commentary stream' is the definition.
(discussion on a forum or social network)
'harsha's first in march' is the wordplay.
'harsha's first' becomes 'h' (1st letter of 'harsha').
'in' indicates putting letters inside.
'march' becomes 'tread' (I've seen this before).
'h' going into 'tread' is 'THREAD'.
(Other definitions for thread that I've seen before include "Filament; connecting link" , "Thin yarn" , "Length of spun cotton or wool" , "Strand of cotton or other fibre" , "Cord - Internet chat room discussion" .)