I Don't Suppose...
...that the owner filed charges against the shoplifter?
I realize that this doesn't make the fact that he was brought up on charges of assault any less grating.
But, to the person who mentioned it being alright to steal, and not alright to assault a person stealing from you...
First of all, it's not alright to steal, but if you don't file a report, nothing's going to happen about it. People are arrested for stealing every day, so clearly the police do in fact do something about it.
You can file a report even if the person you're reporting is charging you with assault. If you don't, when given the opportunity (the police will typically understand that you couldn't file promptly given a serious stab wound) then it makes you look guilty. It doesn't sound like this individual filed a report... it sounds like he took off after a gang of kids and got what his idiocy merited him, as well as lowering himself to their level. I don't know about you, but my life is worth more than cash, candy, or whatever the hell those kids took.
As far as the shopkeeper only defending himself, how do we know that? We have nothing other than this shopkeeper's word. If evidence shows that he acted in self-defense, he will be aquitted. That, however, is up to the courts to determine, as in every other case of reported assault.
Here's a thought. Maybe the shopkeeper got tired of young punks breaking into his store and stealing things. Maybe he'd been robbed before, and didn't report it then either, and the thefts continued because he'd forged himself an unfortunate reputation for being an easy mark. Reporting a crime isn't just an 'option,' it is your duty as a citizen to notify the police of such wrongdoing. Police do not have sensors in the 21st century.
So, the owner got angry, and punched the kid. Y'know what? I've seen it happen, and it's not all that outlandish a story. And I don't care how many mars bars a dumb kid stuffs in his pocket, or how many expensive new DVDs he walks out the door with; that gives you the right as a shop owner to call the police, but not to lay a hand on him, and certainly not to attempt to injure him--the former is often in fact forgiven in America today.
I'm not saying that this is exactly what happened. For all I know, the kid might've stabbed the guy for the fun of it before he even bothered to rob the place, and the punch was a last desperate effort to fight back. All the police are going to see, regardless, is one guy with a stab wound and a kid with a bruise, and both claiming self-defense. They cannot, no matter how ratty or greasy the kid might be, make generalized presumptions about who's guilty and who's innocent, and it doesn't help the idiot shopkeeper that the kid filed a report like you're supposed to whilst that guy went chasing after a gang of thugs like a lunatic.
If the punch was self-defense, it's going to be found that way. Forensics is very advanced at this point in time, but it's still necessary to go through all the phases of legality. People are wrongly accused in serious crimes where a lot of evidence needs to be taken into consideration, the crime is usually covered up, and the criminals involved attempt to deliberately mislead the police.
Criminals do not have more rights than their victims. They have exactly the same ones, until proven guilty in a court of law, and their rights must be respected until they are proven guilty, as with any other individual. Arbitrarily shooting any 11-year-old who pockets a Milky Way or flips the birdie to a shopkeeper is murder, potentially mass murder, and rightly so.
I for one am much happier living in a society with a legal code like what America has today, than living in one where gangs of people beat each other on the back and then run around shooting petty thieves and other minor criminals. All it takes is one shouted word and the wrong impression, and you're gunning down innocents on the spot. The whole reason things are the way they are is so that no judgement, however apparently obvious it might be or whatever the at-first-glance nature of the people involved, is reliant upon the opinion of a single person.