A 21-year-old male supporter has been arrested by South Yorkshire police after emerging onto the pitch during a 1-1 draw between Sheffield and Leeds United on Friday and hitting the shot-stopper in the face.
"That lad could have had a blade," said Foster. "It is ridiculous if you think of it like that. It is a bit scary to be honest with you. I hope the law comes down heavily.
"I wish Chris would have flattened him. I wish he had stood up and given him a boot up the a***."
The Football Association announced yesterday that they are also investigating the incident.