These kind of hops require a good balance control and must not be attempted by novice gymnasts on a high beam.  After the athletes have demonstrated acceptable proficiency on a low beam they can progressively move a skill to a medium beam and later on to a regulation height beam.  Any type of basic drill hopping on one single leg should be trained on support feet.  Notice how this athlete was kicking with the right leg up first  and then comes back kicking with the left leg up.