Caesar upset rep in his city (7)
I believe the answer is:
emperor
'caesar' is the definition.
(I've seen this in another clue)
'upset rep in his city' is the wordplay.
'upset' says the letters should be written in reverse.
'in' indicates putting letters inside.
'his city' becomes 'rome' (I am not sure about this - if you are sure you should believe this answer much more).
'rep' inserted inside 'rome' is 'rorepme'.
'rorepme' reversed gives 'EMPEROR'.
Can you help me to learn more?
(Other definitions for emperor that I've seen before include "Say, Nero" , "Powerful ruler" , "Purple --; -- penguin" , "Beethoven piano concerto, Op. 73" , "Male ruler of a group of countries" .)