Referee nearly dislocated joint (6)
I believe the answer is:
reefer
'joint' is the definition.
(informal term for a marijuana joint)
'referee nearly dislocated' is the wordplay.
'nearly' means to remove the last letter.
'dislocated' indicates anagramming the letters.
'referee' with its final letter taken away is 'refere'.
'refere' anagrammed gives 'REEFER'.
(Other definitions for reefer that I've seen before include "Jack < 's joint" , "A wool jacket; a spliff" , "Midshipman (sl.)" , "packed with cannabis?" , "habit?" .)