Assuming as a name when one's business is collapsing (5,5)
I believe the answer is:
going under
'assuming' is the definition.
The definition and answer can be both to do with motion as well as being present participle verbs.
Maybe there's an association between them I don't understand?
'a name when one's business is collapsing' is the wordplay.
I cannot quite see how this works, but
'name' could be 'gun' and 'gun' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'when' could be 'on' (I've seen this in other clues) and 'on' is found within the leftover letters.
This may be the basis of the clue (or it may be nonsense).
'as' acts as a link.
Can you help me to learn more?
(Another definition for going under that I've seen is " Sinking, failing".)