In favour of tirade against underground being filled to bursting (11)
I believe the answer is:
protuberant
'filled to bursting' is the definition.
(protuberant means bulging out)
'in favour of tirade against underground' is the wordplay.
'in favour of' becomes 'pro' (being pro a particular cause).
'tirade' becomes 'rant' (both can mean an angry outburst).
'against' is a charade indicator (letters next to each other).
'underground' becomes 'tube' (the London Underground is nicknamed the Tube).
'rant' put after 'tube' is 'tuberant'.
'pro'+'tuberant'='PROTUBERANT'
'being' acts as a link.
(Other definitions for protuberant that I've seen before include "Sticking out" , "Outstanding" , "Proud" , "Bulging" .)