Yes, it’s badly written.
Here’s why. The usual formula for self-defense law is that the accused, the guy on trial, has to prove at least the basics of self defense. Then, after he’s made that basic case, the prosecution has to disprove him, beyond a reasonable doubt. The usual process puts the fact-finding in court, before a judge and jury.
This law says a person who has used force “is immune from criminal prosecution.” And it specifically defines “criminal prosecution” to mean “arresting, detaining in custody, and charging or prosecuting the defendant.” See that? He’s immune from even being arrested.
The only way around that is for the police agency to determine that probable cause exists that the use of force was unlawful. In other words, this is not your usual “is there probable cause to believe a crime was committed” but rather “is there specific information about the use of force that makes it probable that the force used was unlawful?”
That is literally what the law says:
This law puts the cart before the horse, in other words. what would normally be developed after arrest, interrogation, charging, etc., now must be essentially an one-the-scene determination by the police.
It’s crazy.
Does that help, without being too technical?