Police stated after the match that the missile, a four inch metal tube, was thrown from outside the ground and landed very close to Shrews keeper Ian Dunbavin.
"It's a wicked looking bit of metal," said superintendent Peter Wright to Five Live.
"If it had exploded anywhere near the goalie or indeed anywhere else in a ground that's packed with 8,000 people, very serious injury or worse could have occurred.
"I just think it's sheer lunacy."
