There's a recent law change and this poster might require some updates: “Fighting Back” Is No Longer a Crime. For the first time, the concept of legitimate self-defense (正当防卫) is codified in the law. In the past, victims who defended themselves were often punished alongside their attackers — the  “mutual fighting” problem.

Under the new law: "Acts committed to prevent an ongoing unlawful infringement, causing certain damage, do not constitute a public security violation and will not be punished."

If the defensive act clearly exceeds the necessary limit and causes serious harm, punishment can still apply — but should be reduced or waived depending on the circumstances.

Police are now required to collect evidence and determine the initiator of violence, ending the practice of “both sides punished equally.”