Crows, for example, about all I messed up in sport (9)
I believe the answer is:
billiards
'sport' is the definition.
(I have seen 'Indoor sport ' mean 'billiards' so perhaps 'sport' could also mean 'billiards')
'crows for example about all i messed up' is the wordplay.
'crows for example' becomes 'birds' (crow is a kind of bird).
'about' means one lot of letters goes inside another.
'messed up' indicates anagramming the letters.
'all'+'i'='alli'
'alli' anagrammed gives 'llia'.
'birds' enclosing 'llia' is 'BILLIARDS'.
'in' acts as a link.
(Other definitions for billiards that I've seen before include "Game with three balls" , "Indoor sport" , "Game played with balls on table with pockets" , "Table game at which Mary Queen of Scots excelled" , "Ball game" .)