Very foolish person, the head, facing trial (7)
I believe the answer is:
nutcase
'very foolish person' is the definition.
(I've seen this before)
'the head facing trial' is the wordplay.
'the head' becomes 'nut' (informal term for somebody's head).
'facing' is a charade indicator (letters next to each other).
'trial' becomes 'case' (I've seen this in other clues).
'nut'+'case'='NUTCASE'
(Other definitions for nutcase that I've seen before include "fool" , "Mad or foolish person" , "Foolish/mad person" , "Maniac - shell" , "Crackpot" .)