Mate runs in addict (6)
I believe the answer is:
friend
'mate' is the definition.
(mate can mean a friend)
'runs in addict' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'in' indicates putting letters inside.
'addict' becomes 'fiend' (fiend can mean someone addicted to something).
'r' inserted within 'fiend' is 'FRIEND'.
(Other definitions for friend that I've seen before include "One who gives proof of genuine regard" , "Person with whom you have a bond of mutual affection" , "Supporter of cause" , "Pal or buddy" , "Comrade for finder" .)