2 directions for each contact. But I believe extreme examples often provide insight, as this example has for movement, footwork, contact zone, and power delivery methods in earlier Steps . After all, when you start a rally by bouncing and stepping into the ball, you're enacting 2 direction for 1 contact, on a slower basis. The swing has the potential of ruining the body's foundation and support, Step 5 . The swing's trajectory is basically an arc.
Arcs accelerate from a common origin in a direction inward from their trajectory.
The common origin is our shoulder to begin with, and the direction inward means inward from the contact spot, 6D, which is why 6B's head-on stroking direction feels solid and strong. This direction inward from the contact spot sends the ball back in the same direction, often more to that one side. There are times when you send the ball outward from the contact spot. Generally speaking, hit your best shot, through the middle of the ball. If you choose not to, understand the risk involved and don't go all out.