Switching arena - Bill is a dancer (9)
I believe the answer is:
ballerina
'dancer' is the definition.
(ballerina is a kind of dancer)
'switching arena bill' is the wordplay.
'switching' indicates anagramming the letters.
'arena'+'bill'='arenabill'
'arenabill' with letters rearranged gives 'BALLERINA'.
'is a' acts as a link.
(Other definitions for ballerina that I've seen before include "girl on point duty" , "lass good at splits?" , "She's a classical dancer" , "Danseuse" , "Female dancer, could be prima" .)