Fast Australian runner behind rival (7)
I believe the answer is:
emulate
'rival' is the definition.
(I've seen this in another clue)
'fast australian runner behind' is the wordplay.
'fast australian runner' becomes 'emu' (I've seen this in another clue).
'behind' becomes 'late' (as in behind schedule).
'emu'+'late'='EMULATE'
(Other definitions for emulate that I've seen before include "Imitate - rival" , "Model oneself on" , "Try to equal or surpass (someone)" , "Try to equal or excel" , "Imitate, try to equal" .)