Match official concerned with foul, primarily (3)
I believe the answer is:
ref
'match official' is the definition.
(referee)
'concerned with foul primarily' is the wordplay.
'concerned with' becomes 're' (re can mean regarding or about).
'primarily' says to take the initial letters.
The first letter of 'foul' is 'f'.
're'+'f'='REF'
(Other definitions for ref that I've seen before include "In brief, he controls a soccer match" , "A diminutive umpire in soccer or boxing" , "One traditionally in black" , "Sports official (abbrev.)" , "Sports umpire" .)