Let's meet up again...I'm going to ignore the basic anatomy in this one, since that's something that comes with observation, practical application, practice, and french fries.
You've got a good setup here, with some great action going on. What keeps it from being as "popping" as it could be lies in the foreshortening and proportion. The biggest is in the hand and kunai, as the hand is large and the knives, which seem to be thrown, are smaller and keep the eye from establishing that they were thrown by the hand. What could fix this is making the knives larger.
Another point in the foreshortening is how big the arm and shoulder of the acting hand are, though I can very well tell where the elbow is, which is a very good thing. Keeping the shoulder and arm smaller up to about the elbow and wrist will give your drawing more depth, and heightening the action.
You've done a great job drawing the actual hand, and the basic pose works pretty well. Overall a pretty good piece!
...in Paradise.
