Scramble as the man blocks pincer movement (8)
I believe the answer is:
encipher
'scramble' is the definition.
(to scramble is to encrypt or encipher a message)
'the man blocks pincer movement' is the wordplay.
'the man' becomes 'he'.
'blocks' indicates putting letters inside (the inside letters form a 'blockage').
'movement' indicates anagramming the letters.
'pincer' with letters rearranged gives 'encipr'.
'he' placed into 'encipr' is 'ENCIPHER'.
'as' acts as a link.
(Other definitions for encipher that I've seen before include "Convert ordinary language into code" , "Put into code" , "Convert to coded form" .)