I think we should teach children to do a correct seoinage before introduce
them in that kind of variant. Only then, they are prepared to make that kind
of variants.

In Spain, it is not allowed to do any technic from mat. Both knees on mat at
the first time, it is called matte and referee gives a verbal warning to
infractor. Next time, it is shido.

As referee, a bad made drop knee seoi nage for me is a shido (false attack).

Best regards

Angel