Awkward person puts it in propeller (3)
This clue is a double definition.
'awkward person puts it in' is the first definition.
(an interfering person 'sticks their oar in')
'propeller' is the second definition.
(I've seen this before)
(Other definitions for oar that I've seen before include "spoon?", "Propelling blade", "Crewman", "Rower's paddle", "Manual boat propeller".)