Heading off, applauded what 3 did? (6)
I believe the answer is:
lapped
'what 3 did?' is the definition.
I can't judge whether this defines the answer.
'heading off applauded' is the wordplay.
'heading off' means to remove the first letter.
'applauded' becomes 'clapped' ('clap' can be a synonym of 'applaud').
'clapped' with its initial letter taken off is 'LAPPED'.
(Other definitions for lapped that I've seen before include "Made extra circuit" , "Washed or flowed against" , "Circuited" , "Scooped up with the tongue" , "Took up with the tongue" .)