The rules of the spear throw are simple.
1. Pick up the spear
2. Throw it.
3. The aim is to make sure it sticks in the target or goes through the center of the tire as done in Australia.
Failure to do so will incur in 30 wonderful burpees. Out of all the Spartan Races I've done, I currently hold a personal record of 5/7 successful throws (as of Oct 2015). Watching Youtube videos from the pros helped as well as incorporating the few tips below. So if you want to ace the spear throw on your next race, here are some things to keep in mind.
Think of it like a mental checklist:
1. Hold the middle of the spear in a fist, not with just your fingers
2. Make sure it's balanced. If you're holding too close to the front, it will be back-heavy and will go high. And vice versa for if the grip is too far back.
3. Keep your fist at eye-level or slightly below.
4. A run up is not necessary as too much force will cause it to go off balance and/or bounce off the target. If the target is far, throw your upper body into the apex of the throw.
5. Time your breathing with the throw.
6. Take your time because you only have one shot.
7. Fix your eyes on where you want to throw it.
This video will give you a good understanding of the technique needed.
If the spear is teetered, I recommend watching this video as it helped me immensely during my races.
Cliffnotes version of the video:
1. Make sure all the rope is on the other side of the fence.
2. Hold a bit of the rope loosely with the spear.
3. Incorporate tips above
4. Let it fly.
And basically practice, practice, practice. With enough practice, once the movements are ingrained in your muscle memory, it would help make this obstacle a breeze and one you can conquer, anywhere, anytime. Bye bye burpees.