Protection by chap leading queen (5)
I believe the answer is:
cover
'protection' is the definition.
(something that protects or shields)
'chap leading queen' is the wordplay.
'chap' becomes 'cove' (British slang term).
'leading' is a charade indicator (letters next to each other) (some letters go in front of others).
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'cove'+'r'='COVER'
'by' acts as a link.
(Other definitions for cover that I've seen before include "Encompass" , "Conceal, screen" , "Extend over (an area)" , "Overlay" , "Disguise" .)