Companion in riotous sector (6)
I believe the answer is:
escort
'companion' is the definition.
(I know that escort is a type of companion)
'riotous sector' is the wordplay.
'riotous' is an anagram indicator.
'sector' with letters rearranged gives 'ESCORT'.
'in' acts as a link.
(Other definitions for escort that I've seen before include "Ford car, first produced in 1968" , "One who accompanies, for protection or as an honour" , "17 [DESTROYER]" , "Chaperone - Cortes (anag)" , "Companion, perhaps for protection" .)