Sends back chap entering Red Square (7)
I believe the answer is:
remands
'sends back' is the definition.
('remand' can be a synonym of 'send back')
'chap entering red square' is the wordplay.
'chap' becomes 'man' (I've seen this before).
'entering' indicates putting letters inside.
'square' becomes 's' (this might be a standard abbreviation which I don't know about).
'man' inserted into 'red' is 'remand'.
'remand'+'s'='REMANDS'
(Other definitions for remands that I've seen before include "Sends back" , "Returns prisoner to custody while further evidence is sought" , "Returns to custody pending further evidence" , "Consigns to prison to await trial" , "Returns prisoner to custody while investigation proceeds" .)