Father maintaining one is a problem (5)
I believe the answer is:
facer
'problem' is the definition.
(I have seen 'Awkward problem' mean 'facer' so perhaps 'problem' could also mean 'facer')
'father maintaining one' is the wordplay.
'father' becomes 'fr' (abbreviation as in a priest's title).
'maintaining' indicates putting letters inside (inserted letters are held or maintained).
'one' becomes 'ace' (ace has a value of one in some card games).
'fr' placed around 'ace' is 'FACER'.
'is a' is the link.
(Other definitions for facer that I've seen before include "Informally, a sudden great difficulty" , "sudden problem" , "Unexpected and difficult problem" , "challenge" , "A sudden serious difficulty" .)