Sudden increase in material being broadcast (5)
I believe the answer is:
surge
'sudden increase' is the definition.
(I've seen this before)
'material being broadcast' is the wordplay.
'material' becomes 'serge' (serge is a kind of material).
'being broadcast' indicates a 'sounds like' (homophone) clue (how the word might sound on the radio or TV).
'serge' sounds like 'SURGE'.
'in' acts as a link.
(Other definitions for surge that I've seen before include "Well up" , "Sudden rapid rise" , "Rapid increase; powerful movement" , "Suddenly increase" , "Sudden upward movement" .)