Line up in entry to perform pirouette (6)
I believe the answer is:
gyrate
'to perform pirouette' is the definition.
(to pirouette can mean to spin or rotate)
'line up in entry' is the wordplay.
'line' becomes 'ry' (abbreviation for railway).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'in' indicates putting letters inside.
'entry' becomes 'gate'.
'ry' reversed gives 'yr'.
'yr' placed into 'gate' is 'GYRATE'.
(Other definitions for gyrate that I've seen before include "Dance wildly" , "Wind in a spiral" , "Go round" , "Move in a circle or spiral" , "Revolve, whirl" .)