Performer juggling car and boat (7)
I believe the answer is:
acrobat
'performer' is the definition.
(I have seen 'Gymnastic performer ' mean 'acrobat' so perhaps 'performer' could also mean 'acrobat')
'juggling car and boat' is the wordplay.
'juggling' is an anagram indicator (I've seen this in other clues).
'and' means one lot of letters go next to another.
'car' after 'boat' is 'boatcar'.
'boatcar' with letters rearranged gives 'ACROBAT'.
(Other definitions for acrobat that I've seen before include "Rope-dancer" , "Agile circus performer" , "Gymnastic performer" , "Tumbler" , "Circus star" .)