Block of drugs including speed seized at the start (7)
I believe the answer is:
eclipse
'block' is the definition.
(I've seen this before)
'drugs including speed seized at the start' is the wordplay.
'drugs' becomes 'ee' (an abbreviation for ecstasy written twice).
'including' indicates putting letters inside.
'speed' becomes 'clip' (clip can mean something's speed).
'at the start' suggests taking the first letters.
The initial letter of 'seized' is 's'.
'clip'+'s'='clips'
'ee' enclosing 'clips' is 'ECLIPSE'.
'of' is the link.
(Other definitions for eclipse that I've seen before include "Lunar/solar phenomenon" , "Solar/lunar phenomenon" , "Surpass, outshine" , "Obscure light from (other celestial body)" , "Obscurement of one heavenly body by another" .)