This type of throw is unique and requires that you practice quite a bit off the course. It is also commonly referred to as the hammer, or Tomahawk throw because the motion resembles the throwing of a Tomahawk. The grip used for this type of throw is just like for the forehand, but the toss offers a unique flight pattern and this makes it ideal for getting over or around certain obstacles.
For example, if you are standing on the opposite side from your target with a small building, such as a restroom facility in your way, you may not want to have to incur extra strokes just to get around the obstruction, and still end up the same distance from the basket as you are at this moment. In this case, the overhand throw would benefit you well. Being able to toss the disc over the roof, and as long as the disc flattens out properly, you can take the obstacle out of the equation.
The stand that should be used for this is the same as for the forehand or side arm throw. A straddle or foot forward stance is best. The windup is essentially the same as for the side arm except that the arm would be brought over the shoulder, above the head.