Left revolutionary in charge of hot line? (6)
I believe the answer is:
tropic
'hot line?' is the definition.
(the tropics are hot regions of the Earth)
'left revolutionary in charge' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'revolutionary' shows that the letters should be reversed in order.
'in charge' becomes 'ic' (abbreviation for 'in charge').
'port' backwards is 'trop'.
'trop'+'ic'='TROPIC'
'of' is the link.
(Other definitions for tropic that I've seen before include "One of two lines" , "Parallel of latitude about 25o N or S" , "Capricorn, say" , "Latitude 23 and a quarter 26 N or S" , "Line bordering hot region" .)