Challenged on interrupting father (5)
I believe the answer is:
dared
'challenged' is the definition.
(daring is a kind of challenging)
'on interrupting father' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'interrupting' is an insertion indicator.
'father' becomes 'dad' (informal term for father).
're' going inside 'dad' is 'DARED'.
(Other definitions for dared that I've seen before include "Made bold" , "Acted with courage - or dread?" , "Challenged (to a deed)" , "Took a risk" , "Ventured" .)