Scots head after a role in discriminatory system (9)
I believe the answer is:
apartheid
'discriminatory system' is the definition.
(historical system in South Africa)
'scots head after a role' is the wordplay.
'scots head' becomes 'heid' (Scottish dialect for 'head').
'after' says to put letters next to each other.
'role' becomes 'part' (eg a part or role in a film).
'a'+'part'='apart'
'heid' put after 'apart' is 'APARTHEID'.
'in' is the link.
(Other definitions for apartheid that I've seen before include "Social policy of racial segregation" , "enforced separation" , "Tyrannical system in S Africa now abandoned" , "form of rule" , "System of segregation formerly practised in South Africa" .)