A back-to-school "Peace in the City" rally turned out to be anything but peaceful after a gunman opened fire at Isaac Campbell Park in Titusville, Florida.

"We are extremely grateful that nobody else was injured in this incident," Titusville Police Deputy Chief Todd Hutchinson said.

No one but the gunman was injured in the incident. He was taken to a local hospital with life-threatening injuries.

"This suspect opened fire at a crowded public park, this could have been so much worse," Hutchinson said.

Isaac Campbell Park shooting scene secure. One male victim airlifted to local hospital with life-threatening injuries. Titusville Police Detectives on scene conducting ongoing active investigation. pic.twitter.com/ytDfB5AVfd — Titusville Police FL (@TitusvillePD) August 4, 2018

Police say it all started when the gunman got involved in a fist-fight with someone at the park. He then left and came back with a gun.

Officers say the heroic bystander who stopped the gunman won't be charged, according to the state attorney's office "as his actions were within the law based on the preliminary investigation."

The story was reported on the website Blue Lives Matter, where several readers commented in support of "concealed carry" and the Second Amendment's "right to bear arms."

"Gee...another armed citizen saves the day. Good work!" posted LordSeamus.

"What awesome news to hear! NRA...concealed carry...a win-win for life!!!" commented Gramercy.

"Now that is gun control," wrote TheMickster.

Local DJ Dwight Harvey had organized the peace rally and said he just can't believe what happened. He told Florida Today when he heard the shots he thought it was firecrackers at first.

"I turned around and just said, 'Oh no, he's got a gun, he's got a gun,'" Harvey told reporters. He said that's when he told the children to run.

He also praised the person who stopped the shooter, "This was standing your ground, in a situation like this with kids involved..."