Doctor concealing anger when upset in this respect (6)
I believe the answer is:
regard
'this respect' is the definition.
('regard' can be a synonym of 'respect')
'doctor concealing anger when upset' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor').
'concealing' indicates putting letters inside.
'anger' becomes 'rage' (rage is a kind of anger).
'when upset' says the letters should be written in reverse (in a down clue - set, written, up).
'dr' placed around 'rage' is 'drager'.
'drager' reversed gives 'REGARD'.
'in' acts as a link.
(Other definitions for regard that I've seen before include "Think of" , "Watch" , "Relation to" , "hold in respect" , "Care" .)