Spectators admitted crossing line, taking turn and turn about (6)
I believe the answer is:
gyrate
'turn about' is the definition.
'spectators admitted crossing line taking turn' is the wordplay.
'spectators admitted' becomes 'gate' (number of people admitted to a sports ground).
'crossing' means one lot of letters goes inside another.
'line' becomes 'ry' (abbreviation for railway).
'taking turn' shows that the letters should be reversed in order.
'ry' back-to-front is 'yr'.
'gate' enclosing 'yr' is 'GYRATE'.
'and' is the link.
(Other definitions for gyrate that I've seen before include "Spiral about a point" , "Revolve quickly and repeatedly around one's own axis" , "Spin around" , "Move rapidly in a circle" , "Move with a circular motion" .)