Spot on former territory (5)
I believe the answer is:
exact
'spot on' is the definition.
(spot on means exactly right)
'former territory' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'territory' becomes 'act' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ex'+'act'='EXACT'
Can you help me to learn more?
(Other definitions for exact that I've seen before include "Precise - demand" , "Meticulous" , "Precisely accurate" , "Demand, extort" , "Demand and obtain" .)