It appears the origin of the shot(s) that hit two fans at Friday’s White Sox game came from inside the park:

“We’re dispelling a lot of things,” Waller said during a brief media availability. “(A shot) coming from outside is something we’ve almost completely dispelled. We’re still looking at every avenue. It’s still under investigation. Something from inside, it could’ve happened that way. We’re looking at every avenue, exploring every lead and everything that we can get.”

ESPN.com

Could it have been a drone strike? They can make them out of cardboard like material now.