In nature, the whole purpose of hunt is natural selection. The boar wouldn't have killed the deer for sport, but in order to eat it and survive.
So what do the Amazons do? First go to hunt the deer with the express purpose of preventing the boar from preying on the deer (ie to make the stronger animal starve, because apparently if a deer gets bitten to death it's a horrible death, but if a boar starves to death it's A-ok), then after the boar manages to prey on the deer anyway they prevent it from actually eating the deer (effectively making the deer's death completely pointless), and finally they kill the boar (end result: both the weaker animal and the stronger animal are dead. I can hear Mother Nature banging her head agaist a tree).