I don't really have any trouble believing that this Rackers thing is real (even though I haven't seen it), or that that Ronaldinho thing is real, either. Give some elite athletes several takes and nobody there putting pressure on them and I think you'd be surprised at what they can do.
Of course, I also believe that the Tiger Woods golf thing was done in one take, and I believe that
this was real and done in one take, as well.
Here's a guy who's just as amazing as Ronaldinho!
Ronaldinho #2
Here is how that video was done:
1. Ronaldinho does actually kick the ball, obviously. But not into the cross bar, most likely into orbit!
2. There is a guy who gives him back 3 balls. This guy is erased digitally, and so is the ball that goes into orbit.
3. A CG ball is animated in either Maya, XSI or 3D Studio MAX and synchronized to the actual ball when he receives it.
4. The CG match is done perfectly despite the fact the real camera is moving. This is done with a technique called Camera Matching. All the FX guys have to do is measure 3 or 4 points in the field so the animator can model them into the software and then those points are used to animate the virtual camera in the software by automatically tracking the given points in the video.
5. After the matching is done, refining comes. This is where the CG ball and any other virtual element is color corrected, blurred, etc to match the color, texture and illumination of the video.
This is done typically in After Effects, Motion, Shake or Combustion.