It looks like he was putting his hand on the ground to stand up. He's still righting himself in the next panel.
Yes there is a reason. To smooth the transition he makes from crouching to standing. Sometimes you don't need to be that explicit about him going through the process of standing up, but the panel where he's standing is on the next page. Or maybe it needed the panel compositionally. Maybe things were going a little too fast after all those action scenes and he needed to slow things down; make Madara look calm and in charge like it's no big deal that Team 7 is right there. There are pacing choices to be made. The narrative is not exclusively delivered through panel contents, comic pages have many parts to them that the author uses.