Tip over (5)
'tip over' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for upset that I've seen before include "Distressed; overturn" , "Discomfit" , "Surprising result" , "Disturb the balance or stability of" , "Disordered - unexpected defeat" .)
(Other definitions for keel that I've seen before include "Ship's basic longitudinal structure" , "Ship (poet.); its bottom" , "Beam on the hull of a vessel" , "Strut along base of ship" , "Part of ship's frame" .)