Fellow always is hot, running high temperature (8)
I believe the answer is:
feverish
'running high temperature' is the definition.
'fellow always is hot' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'hot' becomes 'h'.
'f'+'ever'+'is'+'h'='FEVERISH'
(Other definitions for feverish that I've seen before include "hectic" , "restless state" , "Suffering from a high temperature" , "Extremely excited" , "Restless with excitement or agitation - got ague?" .)