Rules lines scratching head (6)
I believe the answer is:
orders
'rules' is the definition.
(order is a kind of rule)
'lines scratching head' is the wordplay.
'lines' becomes 'borders' (border is a kind of line).
'scratching head' means to remove the first letter.
'borders' with its first letter removed is 'ORDERS'.
(Other definitions for orders that I've seen before include "taken by clergymen" , "directions" , "Monastic societies" , "Holy - -" , "Dictates, decrees" .)