Yet undetermined will be whether a four-month experiment that ends just before the official games will allow Muslim women soccer players to wear specially Dutch-designed hijabs – traditional scarves that allow only the face to be seen. The experiment is to test whether the new design will keep the hijabs in place, not obstructing vision or falling off, posing a tripping hazard. Peripheral vision is crucial in soccer and cannot be obstructed by a scarf, which tends to come loose in competitive play, particularly since hitting the ball with the head is a key tactic -- and any protection on the head gives an unfair advantage.