Do stop or crash into the jamb (8)
I believe the answer is:
doorpost
'the jamb' is the definition.
(doorpost is a kind of jamb)
'do stop or crash' is the wordplay.
'crash' indicates an anagram.
'stop'+'or'='stopor'
'stopor' with letters rearranged gives 'orpost'.
'do'+'orpost'='DOORPOST'
'into' is the link.
(Other definitions for doorpost that I've seen before include "Upright part of entrance frame" , "Jamb" .)