Kansas City magistrate imprisons duke (5)
I believe the answer is:
dodge
'kansas city' is the definition.
(I've seen this before)
'magistrate imprisons duke' is the wordplay.
'magistrate' becomes 'doge' (doge is a kind of magistrate).
'imprisons' means one lot of letters goes inside another.
'duke' becomes 'd'.
'doge' enclosing 'd' is 'DODGE'.
(Other definitions for dodge that I've seen before include "Avoid by a quick move" , "Evasion" , "Avoid with subterfuge" , "Avoid cunningly" , "Ploy" .)