Apprehended a leftist, seizing others (8)
I believe the answer is:
arrested
'apprehended' is the definition.
('arrest' can be a synonym of 'apprehend')
'a leftist seizing others' is the wordplay.
'leftist' becomes 'red' (red is a kind of leftist).
'seizing' is an insertion indicator.
'others' becomes 'rest' (I've seen this before).
'red' placed around 'rest' is 'rrested'.
'a'+'rrested'='ARRESTED'
(Other definitions for arrested that I've seen before include "Stopped or slowed down progress" , "Stopped - took into custody" , "Taken into custody, being serrated" , "Apprehended by police" , "Seized and took into custody" .)