I did realise it was a SCENARIO, however it was rather a different scenario to the actual crime scene that the father came upon in this instance, which is what I thought we were pondering.
I posted the link because I thought it was interesting to see the advice from a British point of view on how much force one can reasonably use as to what would be considered disproportionate.
This is America, of course, where the CJS is different.
If, for instance, someone took it into their head to avenge an alleged crime on information received that would be wrong. It would be wrong to go and chase someone down the street as in Penstemmon's scenario and attack them; however I think it would be right to chase and to apprehend them if possible and restrain them with reasonable force and hope that someone would contact the authorities who could then take over. However, if that left the victim unattended then the victim would be your first concern and you would stay with them and call the authorities.
If, however, DIFFERENT SCENARIO, you found someone attacking your child or a member of your family in your home I think a lot more force could be used without it being dispropotionate.
However, as I said before, none of us know what our 'gut reaction' would be if we came upon a scene like this involving a member of our family, particularly a child.