Defenders are a strong type of Xenomorph that can actually deflect the strongest of ammunitions with its carapace, wrists and probably legs. Those body parts possess very strong and thick chitinous armour which makes it an obvious danger.
This type doesn't use its forelegs, which are actually formed as arms, in its crawling movement; rather it moves like a humanoid which means it is a bipedal type. It is best to defeat it with strong weapons or skilled martial arts (as depicted in the game). All in all, its service is for gathering hosts and defending the hive just as any other Drone, only with a nasty capability to defend itself making it a rather more dangerous type than others.