Destroy his model accidentally (8)
I believe the answer is:
demolish
'destroy' is the definition.
(I know that demolish is a more specific form of destroy)
'his model accidentally' is the wordplay.
'accidentally' is an anagram indicator (a chaotic or accidental ordering of the letters).
'his'+'model'='hismodel'
'hismodel' is an anagram of 'DEMOLISH'.
(Other definitions for demolish that I've seen before include "Pull or tear down" , "Bulldoze" , "Break down" , "Raze to the ground" , "Destroy completely" .)