Traitor to go round with Tom catching ball (8)
I believe the answer is:
turncoat
'traitor' is the definition.
(thesaurus)
'go round with tom catching ball' is the wordplay.
'go round' becomes 'turn' (**).
'with' says to put letters next to each other.
'tom' becomes 'cat' (I have seen 'A tom ' mean 'cat' so perhaps 'tom' could also mean 'cat').
'catching' is an insertion indicator.
'ball' becomes 'o'.
'cat' going around 'o' is 'coat'.
'turn'+'coat'='TURNCOAT'
'to' acts as a link.
(Other definitions for turncoat that I've seen before include "'Renegade, traitor (8)'" , "Deserter to opposition" , "Judas" , "treacherous as one?" , "Rat" .)