Protest over Germany imprisoning this writer mounts (4)
I believe the answer is:
demo
'protest' is the definition.
(demonstration)
'over germany imprisoning this writer mounts' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'germany' becomes 'd' (vehicle registration code for Deutschland).
'imprisoning' indicates putting letters inside.
'this writer' becomes 'me' (the person who wrote the clues).
'mounts' says the letters should be written in reverse (I've seen 'mounted' mean this).
'o'+'d'='od'
'od' going around 'me' is 'omed'.
'omed' backwards is 'DEMO'.
(Other definitions for demo that I've seen before include "Show" , "Political protest" , "March (abbr)" , "exhibit" , "Eg, protest march" .)