Cruel but popular chap put in shade (8)
I believe the answer is:
inhumane
'cruel' is the definition.
('inhumane' can be similar in meaning to 'cruel')
'popular chap put in shade' is the wordplay.
'popular' becomes 'in'.
'chap' becomes 'man' (I've seen this before).
'put in' indicates putting letters inside.
'shade' becomes 'hue' (I've seen this before).
'man' placed within 'hue' is 'humane'.
'in'+'humane'='INHUMANE'
'but' is the link.
(Other definitions for inhumane that I've seen before include "Heartless" , "Callous" , "Cruel" , "Not compassionate" .)