Racket around old tub (4)
I believe the answer is:
boat
'tub' is the definition.
(thesaurus)
'racket around old' is the wordplay.
'racket' becomes 'bat' (bat is a kind of racket).
'around' is an insertion indicator.
'old' becomes 'o' (abbreviation).
'bat' going around 'o' is 'BOAT'.
(Other definitions for boat that I've seen before include "Small ship" , "See 12 Down" , "Small vessel" , "cat, for example" , "Water craft" .)