There's nothing illegal about carrying a knife.They should not have carried on for 20 blocks. That was just stupid. Eric should not have punched the teen. The teen that did the stabbing should not have had a knife and should be charged with carrying one at the very least.
I think the teen doing the stabbing should have been charged. He left, came back and stabbed someone because that person was not attacking him but someone else. That is not SELF defence.