Matthews started researching several different sports and found different types of handedness in each. By the way, he uses "handedness" to refer to the dominant side for feet and eyes as well as hands. Anyway, his team measured the hand, feet and eyes of 2,611 players and found that there were really three main types of laterality. Mixed, you work equally well on both sides, both hand and eye. Single, you tend to favour one side but both hand and eye favour the same side. And cross-laterality, a player's hand and eyes favour only one side but they are opposite sides. Let's start with hockey. Matthews found that it was best to be mixed-handed, this is because a hockey stick must be deployed in two directions, it would be a drawback to have hand or eye favouring one side. An interesting finding is that mixed-handed hockey players were significantly more confident than their single-handed counterparts. Things are slightly different in racket sports like tennis. Here the important thing is to have the dominant hand and eye on the one side. This means that there is a bigger area of vision on the side where most of the action occurs. If a player is cross lateral the racket is invisible from the dominant eye for much of the swing. It means that they can only make corrections much later, and often the damage has been done by then.