Help mainly supported by one Umbrian town (6)
I believe the answer is:
assisi
'one umbrian town' is the definition.
(I've seen this in another clue)
'help mainly supported' is the wordplay.
'help' becomes 'assist' (to assist someone is to help them).
'mainly' means to remove the last letter (virtually or mainly the word, but not all of it).
'supported' becomes 'i' (I can't justify this - if you can you should believe this answer much more).
'assist' with its last letter taken away is 'assis'.
'assis'+'i'='ASSISI'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for assisi that I've seen before include "saint from here" , "St Francis's town" , "town, in Italy" , "St Francis was born in this Italian town" , "Town of saintly associations" .)