Man enters top command (6)
I believe the answer is:
Here is my best explanation:
'command' is the definition.
(behest is a kind of command)
'man enters top' is the subsidiary indication.
'man' becomes 'he'.
'enters' is an insertion indicator.
'top' becomes 'best' ('best' can be similar in meaning to 'top').
'he' going into 'best' is 'behest'.
(Other definitions for behest that I've seen before include "(At someone's) command", "Order", "Command, bidding" and "Command - Thebes (anag)".)