Drug about to be taken by referee (8)
I believe the answer is:
medicate
'drug' is the definition.
(I've seen this before)
'about to be taken by referee' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa').
'to be taken by' indicates putting letters inside.
'referee' becomes 'mediate' (I've seen this in another clue).
'c' inserted inside 'mediate' is 'MEDICATE'.
(Other definitions for medicate that I've seen before include "Treat (one) with drugs" , "Give a drug to" , "Administer a drug to" , "Treat with pills, drugs etc" , "Supply drugs" .)