Deadly obstruction originally hampering almost everyone (6)
I believe the answer is:
lethal
'deadly' is the definition.
(I know that deadly can be written as lethal)
'obstruction originally hampering almost everyone' is the wordplay.
'obstruction' becomes 'let' (let can mean a hindrance).
'originally' suggests taking the first letters.
'almost' means to remove the last letter (most of the word but not all of it).
'everyone' becomes 'all' (all people).
The initial letter of 'hampering' is 'h'.
'all' with its last letter taken away is 'al'.
'let'+'h'+'al'='LETHAL'
(Other definitions for lethal that I've seen before include "Deadly dangerous" , "Destructive" , "Noxious" , "Killing" , "describing a killer?" .)