A driver stopped his car to help a woman who was being attacked, police have said.
The 51-year-old was dragged to the ground and threatened by a man with a knife on Mansfield Road in Eston at about 19:00 GMT on Friday.
A man driving a people carrier disturbed the attacker as he tried to take the woman's handbag.
The woman was treated at James Cook University Hospital for cuts and bruising.
Police are asking the driver to contact them, along with a man walking a dog who may have seen the attacker as he ran off.
A second man is believed to be involved and both had been seen acting suspiciously on the road beforehand, Cleveland Police said.