Foreigner set on and beaten up by a Scotsman (8)
I believe the answer is:
estonian
'foreigner set' is the definition.
Although both the answer and definition are adjectives, I cannot see how they can define each other.
'on and beaten up by a scotsman' is the wordplay.
'and' is a charade indicator (letters next to each other).
'beaten up' becomes 'est' (I can't justify this - if you can you should believe this answer much more).
'by' means one lot of letters go next to another.
'a scotsman' becomes 'ian' (common Scottish name).
'on' after 'est' is 'eston'.
'eston'+'ian'='ESTONIAN'
Can you help me to learn more?
(Other definitions for estonian that I've seen before include "From Tallinn, for example" , "One from Tallinn" , "Eastern European" , "Person from Tallinn, say." , "Native of a Baltic republic" .)