A sailor getting upset about one stock controller (5)
I believe the answer is:
riata
'stock controller' is the definition.
(type of rope used to control farm animals or stock)
'a sailor getting upset about one' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'getting upset' says the letters should be written in reverse.
'about' indicates putting letters inside.
'one' becomes 'i' (roman numeral).
'a'+'tar'='atar'
'atar' back-to-front is 'rata'.
'rata' going around 'i' is 'RIATA'.
(Other definitions for riata that I've seen before include "lasso" , "Rope with noose" , "Tiara turned into a cowboy's rope" , "Lariat made from strange tiara" , "Spanish lariat" .)