In his Heiho Okugi Sho translated by Thomas Cleary as Secrets of the Art of Warfare, the famous Yamamoto Kansuke (1501-1561) writes :
In a fight across a doorway, there is an advantage when you are one against many. The advantage is that even though there are many opponents they cannot encircle you to strike. However, if they have time, enemies may come around by another way, so you should keep yourself covered.
About 450 years later, in his book Flashing Steel, Masayuki Shimabukuro Hanshi describes Moniri - a waza used in a particular case of such a situation.
Your
enemies are lying in wait at a narrow entry gate ... Two ambushers are waiting on
the far side of the gate while a third stalks you from behind. This
presents a challenging situation because if you turn to deal with the
attacker to your rear, the two in the front will rush through the
gate behind you. But, if you attempt to pass through the gate all
three will converge on you while you are confined within its
framework...
