Airborne trooper landing on upset Communist marcher (7)

'marcher' is the definition.
('parader' can be a synonym of 'marcher')

'airborne trooper landing on upset communist' is the wordplay.
'airborne trooper' becomes 'para' (abbreviation of paratrooper).
'landing on' is a charade indicator (letters next to each other) (in a down clue, some letters go on top of others).
'upset' says the letters should be written backwards.
'communist' becomes 'red' (red is a kind of communist).
'red' backwards is 'der'.
'para'+'der'='PARADER'