Run quickly, then fall, producing sign of distress (8)
I believe the answer is:
teardrop
'sign of distress' is the definition.
(I've seen this before)
'run quickly then fall' is the wordplay.
'run' becomes 'tear'.
'quickly then fall' becomes 'drop' (I can't explain this - if you can you should believe this answer much more).
'tear'+'drop'='TEARDROP'
'producing' is the link.
Can you help me to learn more?
(Other definitions for teardrop that I've seen before include "It falls from the eye" , "Bit of salty moisture" , "Little sign of regret" , "one running away from viewer" , "Parroted (anag.)" .)