One’s concerned with fouls, primarily? (3)
I believe the answer is:
ref
'one's' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'concerned with fouls primarily?' is the wordplay.
'concerned with' becomes 're' (re can mean regarding or about).
'primarily?' says to take the initial letters (I've seen 'primarily' mean this).
The initial letter of 'fouls' is 'f'.
're'+'f'='REF'
Can you help me to learn more?
(Other definitions for ref that I've seen before include "In brief, he controls a soccer match" , "Sports umpire" , "A diminutive umpire in soccer or boxing" , "Football official (colloq.)" , "In brief, a soccer controller" .)