What extra restrictions apply to every under-18 category?

In all categories for Pre-Cadets, Cadets and under-18s, including those without technical restrictions:

• No using the head to throw. Tori is penalised with shido.
• No using the head to defend a throw. Tori gets any score earned and uke is penalised with shido.
• No reverse seoi-nage. There's no score and the thrower gets a shido. This means turning away while twisting both hands on the same lapel, without controlling uke, so uke can't breakfall and may land on the neck. Normal seoi-nage, where uke can breakfall and tori stays in control, is allowed.
• Kata-sangaku is restricted, except at Level 4 Cadet events:
  • Taking the kata-sangaku grip in standing or on the ground: the referee calls mate.
  • Throwing from the grip (even an attempt), rolling with it on the ground, or locking the neck or controlling with the legs: direct hansoku-make.