We seem to get a lot of odd discussion topics at Titan, but how to win a fight against a kangaroo may be one of the better ones. So let's talk about fight strategy. First off, a kangaroo will posture like it's boxing, but you can't fall into that trap. Their arms may look jacked but they're only there to hold you close. They'll grapple you and hold tight, then rear back on their tail, and do a Mortal Kombat style double kick. Their legs are huge and quite strong, you'll have internal bleeding before long if they trap you like this.
Hopefully you've got a good ape-index (long reach; measured by taking your "wingspan" – outstretched arms, fingertip to fingertip, and comparing that to your height – most humans are about a negative 2-4 inches, lucky few will actually have a positive ape-index, i.e. more wingspan than height). Even if you've got a badly negative ape-index, you've probably got better upper-body reach than a roo. Use that to your advantage, a few good stingers right on their arrogant noses should do the trick.
If boxing fails, we suggest you go Scrappy-style and grapple. Try to stay behind and above, as the tail and legs are to be avoided, low and in-front is a joey's kill zone. Feel free to go all WWF on them, but know that a simple side-headlock or arm-bar may still give them leverage… try a crippler crossface or cloverleaf. If you're feeling extra saucy, go for the crowd-pleasing back-breaker… it may just be alpha enough to scare away any little jacks looking for some follow-up action from you. Remember, the purpose of war is to prevent future wars (Enders Game FTW).
Oh and we ran a few miles.