Said to be right in the head (5)
I believe the answer is:
heard
'said' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'right in the head' is the wordplay.
'right' becomes 'R' (common abbreviation).
'in' is an insertion indicator.
'r' placed inside 'head' is 'HEARD'.
'to be' acts as a link.
Can you help me to learn more?
(Other definitions for heard that I've seen before include "Perceived sound" , "Was told of" , "Listened to (sound)" , "Tried" , "Got to know (of)" .)