Set up party eschewing leadership, in a manner of speaking (7)
I believe the answer is:
dialect
'a manner of speaking' is the definition.
(I've seen this before)
'set up party eschewing leadership in' is the wordplay.
'set up' becomes 'diact' (I can't justify this - if you can you should give a lot more credence to this answer).
'party' becomes 'l'.
'leadership' says to take the initial letters.
'in' is an insertion indicator.
The initial letter of 'eschewing' is 'e'.
'l'+'e'='le'
'diact' placed around 'le' is 'DIALECT'.
(Other definitions for dialect that I've seen before include "Local language variation" , "Regional form of speech" , "Patois" , "Regional form of word" , "Local language version" .)