The rugby examples show better what should be outlawed

The penalty should have to be a multi-step action. The tackle that injured Marc Andrews was a diving tackle and should not be a penalty I don't think. It was a single motion and he had left his feet before making contact.

It seems to me this should be a situation where a player gets to a tackle and is unable to make it, so instead of getting dragged they drop their weight onto the back of the runner's legs. Kind of like a horse collar. Or a late arriver to a gang tackle does it (that seems to be what happens a lot in the rugby videos). Simply leaving one's feet to make a tackle, no matter how the runner and defender land or whatever unfortunate injuries may occur, should be flagged.

Edit: full agreement that trying to enforce this is likely to be a disaster that, like targeting, ends up penalizing unfortunate results more than dangerous acts