Upset when, after a clear run, there's trouble with (8)
I believe the answer is:
overturn
'upset' is the definition.
(synonyms)
'after a clear run there's trouble with' is the wordplay.
I cannot really see how this works, but
'clear' could be 'overt' (both can mean apparent or obvious) and 'overt' is found in the answer.
an anagram of 'run' is 'urn' which is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'when' is the link.
Can you help me to learn more?
(Other definitions for overturn that I've seen before include "Reverse, rescind," , "Reverse; upend" , "Reverse or capsize" , "Invert" , "tip" .)