As has been previously pointed out, this isn't nearly as funny as it looks. The kangaroo is in an attack posture, and is getting ready to rest its weight on its tail (yes it can do this), and pummel the abdomen of the person so grappled. Kangaroos have wickedly sharp, long claws on their hind feet, which they can use to disembowel an opponent. If the worst that happened here is that their camera got smashed, the person in the photo should consider him/herself lucky.