The principle of this toy is to teach about physics kinematics, the fact that Force = mass * acceleration. It would also teach children the importance of safety in football, as well as bring out the competitive nature among kids. 

This toy works as children put on the helmet that has a sensor on the crown. Their task is to hit the dummy as hard as possible (with the greatest force if you will), and to do so in a safe manner. Thus, if they hit with their head, the sensors on the dummy and helmet will detect it, and they will be deducted points. 

This toy would be a bit pricier due to the sensors and a somewhat sturdy helmet. They would not need a normal football helmet that a player would use simply because they are hitting a stationary, padded target - as well as trying not to hit with their head. However, the toy can be used for recreational football teams, in order to make a fun, competitive way to teach football basics - such as tackling and blocking. It would be safe in respect to the fact that it is extremely rare for somewhat to get hurt hitting a tackling dummy. It would also make it safer for children to play football.