The 55-year-old woman was walking down the street between 6:30 a.m. and 7 a.m. when a man punched her in the back of the head, knocking her to the ground, police said.
The man took her purse and drew a knife, investigators said.
The woman told police someone yelled at the attacker, who then ran off with her purse.
Police say they have the initials of the alleged robber.
