Alright, i figured it out by myself. If anybody else is wondering, watch this tutorial: Connect Dots - Adobe After Effects tutorial - YouTube
I used the beam effect to connect two dots. One of these dots got the tracking data of the moving object, while the other dot remains still.
Let's break down this frame. The text layers are not moving, One of the lines is going behind the arm of the player that is reaching the highest. There are four lines attached to four different moving parts if the frame. The shape of the moving parts do not change very much while the lines in the shot are moving, and the footage was shot at a high frame rate so it could be slowed down smoothly in post.
Tools you will need are rotoscoping to mask the line going behind the arm. You only need to mask the part where the arm is in front of the moving line so this could be done by using an animated shape layer or mask on a solid as a track matte for the line.
You would have to track four areas in the frame so you would use AE's track motion 4 times to get the four tracks.
The hand that goes behind the arm with the red sleeve can be automatically tracked until it moves behind the red sleeve then automatically tracked again as it appears on the other side. You can use the same tracker for that and just delete the bad keyframes while the hand is behind the other players arm.
Once you get all 4 track points you can attach each of the four track points to a null or to the end position of something like the Beam effect. You would use one layer and one beam effect for each line.
In this particular shot the movement is all in a straight line and on a predictable path so it may be faster to just set start and end keyframes for the line's position and then make a couple of adjustments in between the start and end keyframes to smooth out the motion.
To learn how to use the Motion Tracker simply type Track Motion in the Search Help field at the top right corner of AE and check out the community resources. It's pretty straight forward. AE's track motion tracks an area of detail and not a point so selecting most of a hand would work a lot better than selecting just the tip of some fingers. You should get the hang of it fairly quickly.
The beam effect is the simplest way to draw a line in AE that has start and end points that can be attached to tracking data with an expression. If you want to use a shape layer then you would animate the path start and end points.
Let us know if any of this helps. It's not a project that will be easy for someone that has not used AE before. Learning to use AE's tracker is fairly straight forward. Animating a path by hand is also fairly straight forward and matching motion using manual animation can be as easy as setting two or three keyframes. It all depends on the shot.
That's a pretty useful little tutorial...the same guy has a great tutorial of a technique using fast blur with smashed alpha level values to create a cool cell effect.
And one during it taught me that masks in AE can be "opened" which may be another method of achieving the effect you wanted. Opening a mask, applying a stroke and "pinning" the ends to this or that.
Hell maybe that's what the beam effect really is, a stroked mask with glow. ??
I wish he made more tutorials.
thanks for taking the time to write the answer! I am not that new to after effects, the beam effect just didn't come to my mind, thanks for helping me out there.
could you send me the link to the tutorial? I have never heard of open masks and really want to try it.