Rasengan 1O1 class!

the 'perfect' form of the rasengan (at least what we've seen so far) is releasing the pressure of the chackra ball at a single spot. the imprefect form of the rasengan is flawed becuase the chackra is released before the moment of impact, so it's sprades over a wider space, but loses most of it's power...

when Jiraya showed Naruto the rasengan for the first time (on the stone chunin), he 'popped' the ball in his hands, which caused the chackra to run wild and windy, which pushed the chunin back but without any serious damage...

so far, Naruto doesn't know what effects the Rasengan has over a human body, seeing how Kabuto took the hit quite well...