A usually satirical disappointment found often in the first film's fandom is that the Predator answers a challenge to honourable combat in such a cowardly manner. The Predator, when faced with this scenario, opts to use his invisibility to sneak up behind Billy and kill him. He draws a massive blade, removes his shirt, and makes it clear to the Predator chasing them that he's challenging him to a one-on-one fight.
In the first film, the character Billy, approaching the climax, decides to make a heroic sacrifice and stand off against the Predator. Rather than hunting solo, they hunt in groups, and in a scene which mirrors one of the most iconic scenes of the first movie, they behave notably differently. Rather than hunt in their prey's natural habitat, they bring them to a game reserve planet. Now, it's never made explicit within the film, but there's strong indication that the Predators in Predators(2010) are of a different clan than the Predator in Predator(1987). So one of the things this movie establishes (As far as film continuity goes, I believe this was already the case in various comics), is that there are varied clans in this weird alien warrior society, and they're occasionally at war with each other, and most notably, different clans have different hunting behaviour, and even slight difference in the 'rules' they seem to follow.
