Such an MND performance would be fundamentally defective (10)
I believe the answer is:
bottomless
'such' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
I don't understand the rest of the clue.
(Other definitions for bottomless that I've seen before include "Having no limits" , "Inexhaustible" , "Unfathomable" , "Quince thus was in a jam" , "without 17 [BEHINDS] !" .)