Unusual demo car men seize (10)
I believe the answer is:
commandeer
'seize' is the definition.
(I know that commandeer is a more specific form of the action seize)
'unusual demo car men' is the wordplay.
'unusual' indicates anagramming the letters.
'demo'+'car'+'men'='democarmen'
'democarmen' anagrammed gives 'COMMANDEER'.
(Other definitions for commandeer that I've seen before include "Take by force" , "Take control of for military use" , "requisition" , "Take control of for military purposes" , "Appropriate" .)