Circus performer to make a run for it, I hear (4)
I believe the answer is:
flea
'circus performer' is the definition.
(as in a flea circus)
'a run for it i hear' is the wordplay.
'a run for it' becomes 'flee' (to run for it is to flee or escape).
'i hear' indicates a 'sounds like' (homophone) clue.
'flee' is a homophone of 'FLEA'.
'to make' acts as a link.
(Other definitions for flea that I've seen before include "Bug" , "little pest" , "Jumping bloodsucker" , "Wingless, jumping insect" , "Bloodsucking parasite" .)