Again, stretch tightly to prevent further movement (8)
I believe the answer is:
restrain
'prevent further movement' is the definition.
'restrain' can be an answer for 'prevent' (restraining is a kind of preventing). I am not certain of the 'further movement' bit.
'again stretch tightly' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'stretch tightly' becomes 'strain' (I've seen this before. I am not sure about the 'tightly' bit.).
're'+'strain'='RESTRAIN'
'to' is the link.
Can you help me to learn more?
(Other definitions for restrain that I've seen before include "Arrest - confine - subdue" , "Prevent (from excess)" , "Stop" , "Keep under control" , "Control - check" .)