Unduly force bar staff to welcome one (8)
I believe the answer is:
railroad
'unduly force' is the definition.
'railroad' can be an answer for 'force' (to railroad someone is to force them). I'm unsure of the 'unduly' bit.
'bar staff to welcome one' is the wordplay.
'bar' becomes 'rail' (rail is a kind of bar).
'staff' becomes 'rod' (both can mean a stick or cane).
'to welcome' means one lot of letters goes inside another (in sense of 'inviting in').
'one' becomes 'a' (a thing is one thing).
'rod' enclosing 'a' is 'road'.
'rail'+'road'='RAILROAD'
Can you help me to learn more?
(Other definitions for railroad that I've seen before include "[DRAGOON]" , "Bully" , "Unfairly force into decision - way for train" , "US term for train line" , "Rush (someone) into doing something" .)