Official report of headless chicken in container (8)
I believe the answer is:
bulletin
This clue might be a double definition.
'official report' is the first definition.
(a news report)
'headless chicken in container' is the second definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'of' acts as a link.
(Other definitions for bulletin that I've seen before include "Newsflash" , "Official statement for publication" , "Regular news up-date" , "Newsletter, report" , "Short and regular up-date" .)