Restrict stuff on page (5)
I believe the answer is:
cramp
'restrict' is the definition.
(cramping is a kind of restricting)
'stuff on page' is the wordplay.
'stuff' becomes 'cram' (cramming is a kind of stuffing**).
'on' means one lot of letters go next to another.
'page' becomes 'p'.
'cram'+'p'='CRAMP'
(Other definitions for cramp that I've seen before include "Severe muscular pain" , "Give too little space to" , "hamper" , "Contract" , "Muscle spasm" .)