[BerntR]

You'd normally tend to think that he looped it under plane. But those guys can hit it with their feet and bodies pointed any which way, right.

Regardless of his plane of motion and the camera angle there should be a symmetry around the drawn plane line before and after low point. If he were swinging on a flat plane, that is. His sweet spot is clearly inside of the drawn line towards impact. Yet he stays on the line past impact. If he were moving the sweeet spot on a flat plane he should be moving outside the line past impact.