Force Fields are protective shields that appear throughout the Star Fox series.
Star Fox Adventures
In Star Fox Adventures, each of the four GateKeepers use an invisible surrounding force field to protect Dinosaur Planet and its disconnected SpellStone locations. Fox must pilot his Arwing through a certain number of Gold Rings in order to deactivate the force field before reaching the end of a path, so that he can fly down into the location. When Fox flies through the required number of Gold Rings, General Pepper notifies him that the force field has been deactivated.
The main Dinosaur Planet requires Fox to fly through a single Gold Ring. Each of the four SpellStone locations increase the required total of Gold Rings, and the final SpellStone location, Dragon Rock, requires Fox to fly through ten Gold Rings. If Fox does not fly through enough Gold Rings on time, he must restart at traveling down the path.