Fish caught at busy centre (4)
I believe the answer is:
chub
'fish' is the definition.
(chub is a kind of fish)
'caught at busy centre' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'at' means one lot of letters go next to another.
'busy centre' becomes 'hub' (eg a transport hub).
'c'+'hub'='CHUB'
(Other definitions for chub that I've seen before include "European freshwater fish" , "Fat freshwater fish" , "Fat relative of the carp" , "River fish; rhymes with public house" , "Thick-bodied river fish" .)