Not stopping in case gun went off (9)
I believe the answer is:
unceasing
'not stopping' is the definition.
(I've seen this before)
'in case gun went off' is the wordplay.
'went off' indicates an anagram.
'in'+'case'+'gun'='incasegun'
'incasegun' is an anagram of 'UNCEASING'.
(Other definitions for unceasing that I've seen before include "Constant" , "Continuous" , "Never ending" , "Never-ending" , "Endless" .)