Police say at least three people jumped out of their cars to rescue the 17-year-old girl when the muttering, incoherent man lunged at her with the knife Friday afternoon near Cloonan Middle School.
Police say she broke free as they struggled, and was not seriously injured.
Police say 47-year-old Ronald Gordon of Stamford was charged with attempted first-degree assault after the bystanders kept him from escaping before officers arrived.
Gordon was taken to Stamford Hospital for evaluation. He was being held on $100,000 bond and is due in Stamford Superior Court on Nov. 5.
Information wasn't immediately available Sunday on whether he had an attorney.