Overturn limit on dimensions (7)
I believe the answer is:
capsize
'overturn' is the definition.
(I know that capsize is a more specific form of overturn)
'limit on dimensions' is the wordplay.
'limit' becomes 'cap' (capping is a kind of limiting).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'dimensions' becomes 'size' (I've seen this in another clue).
'cap'+'size'='CAPSIZE'
(Other definitions for capsize that I've seen before include "Overturn (a boat)" , "Of boat, turn turtle" , "Upset" , "Turn so that keel faces upwards" .)