Crew need underground rock for broadcast (3)
I believe the answer is:
oar
'crew need' is the definition.
(I've seen this in another clue)
'underground rock for broadcast' is the wordplay.
'underground rock' becomes 'ore' (I've seen this in another clue).
'for broadcast' shows a homophone (sound like).
'ore' sounds like 'OAR'.
(Other definitions for oar that I've seen before include "Rowing boat operator" , "Crewman" , "Implement to propel a boat" , "Rowing device" , "Boat propellant" .)