Turn turtle (5)
'turn turtle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for capsize that I've seen before include "Of boat, turn turtle" , "Turn so that keel faces upwards" , "Upset" , "Overturn (a boat)" .)
(Other definitions for upend that I've seen before include "Stand erect" , "Set (something) vertical" , "Topple" , "Tip on side" , "Affect greatly" .)