Ninja had many tools to even the odds in a fight. Kyusho jutsu was one of these. It included pressure-point striking for paralysis and knockouts. The ninja of ancient Japan are portrayed today as assassins and hired killers. For the most part, however, their assignments were those of a spy. Espionage might mean gathering information on troop movements and scouting an area without being seen. It might also mean sneaking into an inner room in a castle and stealing a letter to prove some treachery. If they were seen at all, they had failed, because they would be outnumbered.
Evening the Odds
If a samurai confronted the ninja in the halls of a castle or courtyard, he was almost certainly better armed and armored than the ninja and, quite often, he was not alone. The ninja had to quickly even the odds or he was dead. Kyusho training allowed the ninja to safely engage the samurai with fewer weapons. It might happen like the scenario listed below.
An Ancient Fight
The samurai steps in, swinging his sword to cut the ninja down. Instead of ducking or evading the sword, the ninja steps in closer. To the samurai's surprise, the ninja is too close for his sword to cut. The ninja blocks the samurai's wrist with his left hand and strikes his arm at a point called the Daimon, or "big gate." This is in the fan of muscles that come off the shoulder and control the arm's gross motor functions, like swinging a sword. Then the ninja strikes the Nagare point, or radial nerve, lower in the arm close to the outside of the elbow. This weakens the samurai's grasp on the sword with that arm so that his arm is deadened and can't muster a second attack. Without even turning, the ninja swings his right elbow hard into the Jakkin, or weak muscle point, of the other arm and suddenly the samurai finds both arms useless and in pain. The ninja is free to flee or finish the samurai off.
The descendants of the ninja arts today carry on these paralysis strikes and techniques. In the Bujinkan, founded by Masaaki Hatsumi, there are techniques in Takagi Yoshin Ryu and Koto Ryu that use these very same points. On today's streets, these techniques are as valid as they were in the day of the samurai. Anyone you meet in the dark of night may have a knife or club. The ability to even the odds with these ancient sneaky tricks is still a good survival strategy.