From
https://www.thestar.com/sports/2018/...ury-match.html
Police are investigating the incident and it appears to be firecrackers. I know that I've seen written above and read elsewhere it could have also been a concussion grenade a flare that heated up and exploded a drum. Regardless, it was reckless and could have lead to some serious injuries.
The perpetrators were ejected from the game. Hopefully these 'fans' names were recorded and they will be banned.
Like OgtheDim says, we all want to enjoy watching a game and not have to worry about getting burned from an errant firecracker or flare.