Just like they passed a new law in recent times, that increased the punishments, when firefighters and medics etc. gets attacked during work. Sounds good as well, I mean, what asshole would attack medics and firefighters?!?
The thing is just, that the law also applied to policemen. So when you are in a demonstration, peaceful and are about to get hit by the police who decided to end the demonstration with force, and your reflexes push back - then you can get prosecuted with a law that was advertised to protect firefighters.
"Schutzwaffen", i.e. protective weapons
https://de.wikipedia.org/wiki/Schutzwaffe
This includes the thing boxers put in their mouth to protect their teeth... let that sink in. Carrying something like that to a protest already is a crime, maximum sentence is 1 year.
edit: just saw an earlier comment with more info: https://news.ycombinator.com/item?id=21158544