No, actually, he's not.
He was charged with burglary in 2012, but the charges were dismissed.
While they are hardly the "end all" when it comes to supporting an argument, according to Snopes, Grosskreutz is no such thing. He was charged with burglary in 2012 (he was a minor) but the charges were dismissed. Also, if he was a felon, he'd be facing charges for illegal possession of a firearm by a felon...
What’s True and False About Kyle Rittenhouse’s Alleged Victims
Actually Grosskreutz was not a convicted felon, however, the People's Revolution Antifa affiliated anarcho-communist terrorist commander is on video committing a felony.
I saw the video from his cell phone. And I posted it in another thread here at USMB.
Grosskreutz confronted Rittenhouse. And after Rittenhouse told him that he was going to report to the police and started running to the police, Grosskreutz started chasing Kyle and ordered his underlings to "cranium" Kyle.
And that's exactly what the insurgents following his commands did. One ran up behind Kyle and bashed him in the cranium with a weapon. It looked like a rock or something.
That put Kyle on the ground. That vicious attack rung his bell enough to make Kyle lose balance and fall to the ground.
Then another as yet unidentified minion obeying Grosskreutz's loud command to "cranium" Kyle kicked Kyle in the cranium, quickly followed by Huber, who bashed Kyle in the cranium with a weaponized skateboard and attempted to rob him of his firearm, thus earning his Darwin award.
Then the communist insurgent commander got his right bicep instantly transformed into pink mist when he drew a pistol on Kyle.
As far as the crimes he was previously convicted of, there was only 2 that I know about. After previously receiving a warning for going into a police station parking lot and filming their personal vehicles parked there, he came back again and was arrested an convicted of prowling.
And on another occasion he was convicted of carrying a firearm in public while intoxicated.