Ill-fitting strides, a catastrophe (8)
I believe the answer is:
disaster
'catastrophe' is the definition.
(I know that catastrophe can be written as disaster)
'ill-fitting strides a' is the wordplay.
'ill-fitting' is an anagram indicator.
'strides'+'a'='stridesa'
'stridesa' is an anagram of 'DISASTER'.
(Other definitions for disaster that I've seen before include "Extreme event resulting in great loss and misfortune" , "Heavy blow" , "complete failure" , "Event causing great damage" , "Catastrophe, calamity" .)