Broadcast hammered — that's beyond dispute (8)
I believe the answer is:
airtight
'beyond dispute' is the definition.
Both the definition and answer are adjectives.
Maybe you can see an association between them that I don't see?
'broadcast hammered' is the wordplay.
'broadcast' becomes 'air' (to air on TV).
'hammered' becomes 'tight' (I can't explain this - if you can you should believe this answer much more).
'air'+'tight'='AIRTIGHT'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for airtight that I've seen before include "securely sealed" , "beyond question" , "With no opening" , "not letting out a breath?" , "Totally sealed" .)