Left back in charge, given latitude (6)
I believe the answer is:
tropic
'latitude' is the definition.
(tropic is a kind of latitude)
'left back in charge given' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'back' is a reversal indicator.
'in charge' becomes 'ic'.
'given' means one lot of letters go next to another.
'port' back-to-front is 'trop'.
'trop'+'ic'='TROPIC'
(Other definitions for tropic that I've seen before include "Line at nearly 23 degrees N or S" , "Parallel of latitude about 25o N or S" , "Capricorn, say" , "Cancer is one, Capricorn another" , "hot spot" .)