Beginning to obstruct launch pad (8,5)
I believe the answer is:
starting block
'launch pad' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'beginning to obstruct' is the wordplay.
'beginning' becomes 'starting' ('start' can be a synonym of 'begin').
'to obstruct' becomes 'block' ('block' can be a synonym of 'obstruct').
'starting'+'block'='STARTING BLOCK'
Can you help me to learn more?
(Other definitions for starting block that I've seen before include "Sprinter's position as race begins" , "Device used by sprinter" .)