Native American quickly casing hotel (6)
I believe the answer is:
apache
'native american' is the definition.
(I've seen this before)
'quickly casing hotel' is the wordplay.
'quickly' becomes 'apace' ('apace' can be a synonym of 'quickly').
'casing' is an insertion indicator (I've seen this in other clues).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'apace' placed around 'h' is 'APACHE'.
(Other definitions for apache that I've seen before include "A peach of an Indian tribe?" , "nickname of US State" , "Native American - French hoodlum" , "member of tribe" , "on the streets of Paris" .)