[There's absolutely no warning or hesitation: Sasuke throws his arm out and snaps his fist at the wrist. The power comes from the swivel in his hips as he steps forward.

He doesn't punch Senri in the stomach so much as his fist just connects. He barely moves his body, but there's quite a bit of force behind the action. It won't hurt or cripple, but it'll definitely sting.]

Always be on guard. Since he won't be without any training, that's the time you need to hit him.

The only thing you need to remember is to punch through him and to punch with your hips. Don't throw it with power from your arm and shoulder. That's pointless. You don't need to move to get the strength to hit someone well.