Some latitude over shot headed by right back (6)
I believe the answer is:
tropic
'some latitude' is the definition.
(tropic is a kind of latitude)
'over shot headed by right back' is the wordplay.
'over' indicates putting letters inside.
'shot' becomes 'drop' (small measure).
'headed' means to remove the first letter (head can mean to remove the top from something).
'by right back' becomes 'tic' (I can't justify this - if you can you should give a lot more credence to this answer).
'drop' with its first letter removed is 'rop'.
'rop' placed inside 'tic' is 'TROPIC'.
Can you help me to learn more?
(Other definitions for tropic that I've seen before include "Capricorn, perhaps" , "Parallel of latitude about 25o N or S" , "One of two parallels north and south of the equator" , "Line defining hot zone" , "Limiting line of torrid zone" .)