Last of runners flash past — don't give up (5,2)
I believe the answer is:
stick by
'last of runners flash' is the definition.
The definition and answer can be both to do with fundamental existence as well as being verbs in their base form.
Maybe you can see a link between them that I don't see?
'past don't give up' is the wordplay.
I cannot really understand how this works, but
'past' could be 'by' (as in years gone by) and 'by' is found in the answer.
The remaining letters 'stick' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for stick by that I've seen is " Support".)