Happened to be the person commanding a dog, like a setter (8)
I believe the answer is:
occurred
'happened' is the definition.
('occur' can be a synonym of 'happen')
'be the person commanding a dog like a setter' is the wordplay.
I cannot quite understand how this works, but
'be' could be 'occur' (synonyms) and 'occur' is located in the answer.
'person' could be 'red' (red is a kind of person) and 'red' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for occurred that I've seen before include "Took place" , "Happened" , "Came to pass" .)