Son, one who blabs -- a sneaky type (7)
I believe the answer is:
stalker
'a sneaky type' is the definition.
(someone who sneaks around)
'son one who blabs' is the wordplay.
'son' becomes 's'.
'one who blabs' becomes 'talker' (someone who talks).
's'+'talker'='STALKER'
(Other definitions for stalker that I've seen before include "Stealthy pursuer" , "Obsessive follower" , "unwanted admirer?" , "One harassing celebrity" , "Person who follows another about as if hunting prey" .)