Hits sources of obstruction clutching bosom (12)
I believe the answer is:
blockbusters
'hits' is the definition.
(a blockbuster is a commercial hit)
'sources of obstruction clutching bosom' is the wordplay.
'sources of obstruction' becomes 'blockers' (things which block or obstruct).
'clutching' indicates putting letters inside.
'bosom' becomes 'bust' (I've seen this before).
'blockers' placed around 'bust' is 'BLOCKBUSTERS'.
(Other definitions for blockbusters that I've seen before include "Bombs" , "successful at the box office? - with 4d" , "screen epics" .)