I disagree.
Most of the jutsus, including chidori, don't use physical force. The only effort that your body is doing when using a jutsu is the hand-seals part, after this the jutsu makes the rest for you. However, I think that your idea could have a better use if you would apply it for chakra. Depending on your HP, the jutsu you perform will have more chakra cost as it would be harder for you to concentrate your chakra while being hurt leading to a chakra loss.
But even so, I don't see any point in implementing this idea yet, as it's only about the realism of the game. Atm, the suggestions should be about balancing the use of chakra with the chakra amount and the chakra regeneration rate. Implementing something like that would only turn this things upside down, requiring new valors for each action.
In that case, 1 kunai to the head should kill you, one sword slice should sever your body. You get my point, as nova said, it would make it hard for a comeback.
This is discussible. I still didn't understand what Vreg means by realistic. There are two types:
1. The realism from real life, where a kunai to the chest (not a frontal trajectory) can get you out of the fight.
2. The realism from naruto, where if you are a high rank ninja, you can receive tens and hundreds of kunais and still be able to hold a kunai with your teeth, be able to run through an army dodging every of their attack and finally stabbing the army leader. (Zabuza)
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