Avon town manager Virginia Egger said that 17 minutes into the 23-minute show, "a shell apparently exploded in its tube rather than firing correctly into the sky."
In videos posted on social media, you can hear the "oohs" and "ahhs" at the town of Avon's fireworks display quickly turn into 'whoas!," and "what is going on?"
"The misfired shell caused the rack of 5"-shells to tip in two directions causing two to three shells to cross into the crowd," said Egger.
A spokesman for Western Enterprises, the production company that put on Avon's annual 'Salute to the USA', said, "a rare product malfunction occurred, causing several adjacent fireworks to misfire."
"Western Enterprises, Inc. deeply regrets that people were injured during the Avon fireworks display," Gary Caimano said in an email. "Public safety has always been our number one priority."
Egger said all nine people who "experienced minor abrasion burns were treated by emergency medical personnel at the show and released."
Greg Daly, Avon's deputy fire chief, said it was "wonderful news that the injuries were very minor."
"The crowd was exceptional in its calm response to what could have been a much more serious incident," said Daly.
Despite the praise for being calm, some in the 20,000-strong crowd took to Twitter to describe their fright.
"I don't think I've ever been so scared watching the Avon firework show," tweeted Hannah Beiersdorf, a student at the University of Colorado. "But I'm glad that we're all safe. I hope everyone else is too."
Western said that all of the pyrotechnic equipment had been properly inspected and approved by the authorities. "We take great pride in our efforts to procure the best product available to use in our fireworks displays."
The company said it would "take immediate action to identify and remove the product that may have contributed to the incident for our remaining Fourth of July displays as a proactive measure."