One engaged in motor madness in coach (8)
I believe the answer is:
carriage
'coach' is the definition.
(I know that coach can be written as carriage)
'one engaged in motor madness' is the wordplay.
'one' becomes 'I' (Roman numeral).
'engaged in' indicates putting letters inside.
'motor' becomes 'car' (informal term for car).
'madness' becomes 'rage' (synonyms).
'car'+'rage'='carrage'
'i' put inside 'carrage' is 'CARRIAGE'.
'in' acts as a link.
(Other definitions for carriage that I've seen before include "Horse-drawn passenger vehicle" , "Bodily posture or wheeled vehicle" , "Deportment; vehicle" , "Posture; conveyance" , "Bearing; part of train" .)