Jerky movements when somersaulting in authentic performance (7)
I believe the answer is:
recital
'performance' is the definition.
(I know that recital is a type of performance)
'jerky movements when somersaulting in authentic' is the wordplay.
'jerky movements' becomes 'tic' (as in a nervous tic).
'when somersaulting' says the letters should be written in reverse (letters flip or somersault over).
'in' means one lot of letters goes inside another.
'authentic' becomes 'real' (I've seen this in another clue).
'tic' written backwards gives 'cit'.
'cit' put inside 'real' is 'RECITAL'.
(Other definitions for recital that I've seen before include "Musician's performance" , "Article found in performance" , "Maybe solo musical performance" , "Solo music performance" , "Performance, usually musical" .)