Father locks up outlaw (6)
I believe the answer is:
pariah
'outlaw' is the definition.
(thesaurus)
'father locks up' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'locks' becomes 'hair' (I've seen this before).
'up' is a reversal indicator (in down clue: letters go upwards).
'hair' in reverse letter order is 'riah'.
'pa'+'riah'='PARIAH'
(Other definitions for pariah that I've seen before include "One is rejected by society" , "Outcast (state)" , "Social outcast" , "An untouchable" , "person shunned" .)