It is important to keep in mind the angle you are viewing the plane from. The only time all the points on a plane will appear in one line is when the point you are viewing it from is in the plane. Example: A number of marbles placed on a tabletop are in the same plane. However, for them to appear in a straight line, the point of view must also be in the plane (tabletop height). If you view them from a point outside the plane (above or below the tabletop), you could draw a number of triangles (from marble to marble) as you drew in the pic.

The camera that shot the pic http://mysite.verizon.net/vzep5xd2/baseballphotosandvideos/id3.html was not in the plane of Bonds’ swing plane. Since his axis of rotation is tilted away from the camera, we are looking slightly up through his swing plane. We must take this into account when discussing points that lie in his swing plane.