All I can say is that it takes place near the very end of the footage when Team Cap and Team Tony are fighting each other - Nat’s on the ground, Clint’s above her, and Nat says “we’re still friends, right?” and Clint responds, “that depends on how hard you hit me”, and that’s it. It’s a pretty playful scene, very banter-ish, very much Clint & Nat, and they’re both grinning at each other. 

I have zero idea about what it means and I don’t want to speculate too much, because it was such a quick little scene. But the tone of it was pretty light.