Pledged to get shelf (5)
I believe the answer is:
ledge
'shelf' is the definition.
(I know that shelf can be written as ledge)
'pledged to get' is the wordplay.
'to get' says the answer is hidden in the clue (I've seen 'gets' mean this).
'LEDGE' can be found hidden inside 'pledged'.
(Other definitions for ledge that I've seen before include "Narrow projecting shelf as from window" , "rocky situation?" , "Shelf-life projection" , "A step" , "Narrow shelf, often attached to window" .)