Playful line about drug in Olympic sport (7)
I believe the answer is:
archery
'olympic sport' is the definition.
(I've seen this in another clue)
'playful line about drug' is the wordplay.
'playful' becomes 'arch' (I've seen this before).
'line' becomes 'ry' (abbreviation for railway).
'about' says to put letters next to each other.
'drug' becomes 'e' (E is another name for ecstasy).
'ry' after 'e' is 'ery'.
'arch'+'ery'='ARCHERY'
'in' acts as a link.
(Other definitions for archery that I've seen before include "Shooting with bows and arrows" , "Arrow-shooting" , "Bowman's sport" , "Target sport - Olympic event in from 1900-08, in 1920 and since 1972" , "Bow and arrow sport" .)