Growing, as I shamble into the arena (7)
I believe the answer is:
raising
'growing' is the definition.
('raise' can be a synonym of 'grow')
'as i shamble into the arena' is the wordplay.
'shamble' indicates anagramming the letters (I've seen 'shambles' mean this).
'into' is an insertion indicator.
'the arena' becomes 'ring' (eg a boxing ring).
'as'+'i'='asi'
'asi' is an anagram of 'ais'.
'ais' put inside 'ring' is 'RAISING'.
(Other definitions for raising that I've seen before include "Bringing up" , "Elevating" , "Promoting (in rank)" , "Growing" , "Lifting" .)