The disposition of fellows in almost completely sober surroundings (11)
I believe the answer is:
temperament
'the disposition' is the definition.
('temperament' can be a synonym of 'disposition')
'fellows in almost completely sober surroundings' is the wordplay.
'fellows in' becomes 'men' (I am not sure about this - if you are sure you should believe this answer much more).
'almost completely' means to remove the last letter.
'sober' becomes 'temperate' (I've seen this in another clue).
'surroundings' indicates putting letters inside.
'temperate' with its last letter taken away is 'temperat'.
'men' placed within 'temperat' is 'TEMPERAMENT'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for temperament that I've seen before include "Person's nature; adjustment in piano tuning" , "Disposition; tuning adjustment" , "A person's nature as it affects behaviour" , "Frame of mind" , "Personality" .)