Organizers of a large paintball event in Ottawa say players were put in serious danger over the weekend, when someone replaced its regular paint-filled pellets with marbles.

Commando Paintball’s annual D-Day event in Ottawa’s east end attracted approximately a thousand players from across North America on Sunday afternoon. The competition was going smoothly with thousands of paintballs whizzing through the air until organizers say the day took a potentially deadly turn.

One player was struck three times in the chest by marbles, according to Gordon Estabrooks, one of the generals in Commando Paintball’s event. He said one of the marbles hit the man in the sternum, which knocked him over.

“A projectile going that fast will kill you or cause some serious, serious injury,” Estabrooks told CTV Ottawa on Tuesday.

Paintballs can reach speeds of anywhere from 260 to 300 km/h when fired.

The player was assessed by first aid teams and was advised to visit a hospital for an X-ray to ensure he didn’t have any broken ribs.

The second player received a bruise on his shoulder after he was struck by one of the marbles.

The event’s organizers immediately cancelled the rest of the game and performed a search of the playing field. They discovered four marbles on the grounds.

One of Commando Paintball’s co-owners, Marie Longtin, said something like this has never happened at their venue before.

“Somebody was shooting marbles, however they were doing it, and that’s not something that’s acceptable,” Longtin said.

The paintball company said they’re conducting an investigation into the incident. They’re offering a $1,500 reward to anyone who can provide information.

Ottawa Police said they’re aware of what happened, but haven’t received a complaint about it yet.

Despite the dangerous turn of events, paintball enthusiast George Dunphy, who attended the D-Day game with his 13-year-old son, said they won’t be deterred from heading back out on to the field.

“I’m probably going out again tomorrow and my son and I are already counting down to the next D-Day,” Dunphy said. “We’re not going to stop.”

With a report from CTV Ottawa’s Matt Skube