Imagine a Harpy Eagle or Crowned Eagle, size it up and you have Haast's Eagle. This bird was so enormous it could kill a Giant Moa. A moa pelvis I found online is, to me, the best evidence that Harpagornis moorei ate moas. It has a very deep gouge in it and a Haast's Eagle talon is the only match. But even this huge eagle could not evade extinction when the Maori came to New Zealand. They competed with the eagle for its prey, the Giant Moa. The Maori hunted the moas to extinction and with no moas to hunt, the Haast's Eagle was starved into extinction.
Some scientists believe that the Haast's Eagle was not only capable but did attack young humans.