Go up and start on cast during a broadcast (6)
I believe the answer is:
ascend
'go up' is the definition.
(synonyms)
'start on cast during a broadcast' is the wordplay.
'start on' indicates taking the first letters (I've seen 'starts on' mean this).
'during' indicates putting letters inside.
'broadcast' becomes 'send' (synonyms).
The first letter of 'cast' is 'c'.
'a'+'send'='asend'
'c' placed within 'asend' is 'ASCEND'.
'and' is the link.
(Other definitions for ascend that I've seen before include "Climb, rise" , "Move upwards" , "Take off" , "Gain height" , "shift to a higher plane" .)