I think there are genuine in the back frees. This can also be very dangerous, I can't fathom a rule that allows free rein to plough into someone's back. But there is no doubt players drop the knees to draw a free. Can often tell but another rule that's very hard to umpire in the heat of the moment.It is very easy, but what is this free designed to stop? As you say its just a free that players milk, its actually a free that serves very little purpose. The only thing it does, is risk the sling tackle more as players need to sling more so as not to fall into their back. If the AFL were actually wanting to protect the head from sling tackles then they should remove the in the back free IMO.