Live broadcast attempt is heartless frivolity (6)
I believe the answer is:
levity
'frivolity' is the definition.
(I know that levity is a type of frivolity)
'live broadcast attempt is heartless' is the wordplay.
'broadcast' indicates anagramming the letters (letters scattered or cast around).
'attempt' becomes 'try' (synonyms).
'is heartless' suggests removing the centre.
'try' with its centre removed is 'ty'.
'live' anagrammed gives 'levi'.
'levi'+'ty'='LEVITY'
(Other definitions for levity that I've seen before include "Playfulness" , "Light-heartedness" , "Light quality" , "Unseriousness" , "Flippant attitude to serious matters" .)