Reason stateside A&E is on the news briefly (5)
I believe the answer is:
infer
'reason' is the definition.
(both can mean to deduce)
'stateside ae is on the news briefly' is the wordplay.
'stateside ae' becomes 'ER' (emergency room, US equivalent to an A and E).
'is on' is a charade indicator (letters next to each other).
'the news' becomes 'info' (I've seen this in another clue).
'briefly' means to remove the last letter.
'info' with its final letter taken away is 'inf'.
'er' after 'inf' is 'INFER'.
(Other definitions for infer that I've seen before include "Draw a conclusion" , "Take finer meaning from" , "Establish by deduction" , "Extrapolate, conclude" , "Deduce, surmise" .)