Catch sight of shapely Hal leaving disguised (4)
I believe the answer is:
espy
'catch sight of' is the definition.
(espying is a kind of catching sight of)
'shapely hal leaving disguised' is the wordplay.
'leaving' indicates named letters should be taken away.
'disguised' is an anagram indicator.
'shapely' with 'hal' removed is 'spey'.
'spey' is an anagram of 'ESPY'.
(Other definitions for espy that I've seen before include "Behold" , "Make out at a distance" , "Spot at a distance" , "Watch" , "Catch sight of (poetic)" .)