Originally Posted by tongzilla

This may sound so idiotic now that Yoda has already confirmed the correct answer. But this is what I think.

Lets start with the first word, "Normally". This says to me that we are looking at the case where both Swingers and Hitters are using the Geometric Straight Plane Line as their Delivery Line (so Hittes are not using their Angle of Approach Delivery Line).

“Cross Line” means something that moves that is not parallel to your Plane Line (normally the Target Line also). “On Line” means something that moves that is parallel to your Plane Line. So what is that ‘something’?

"Delivery Thrust is Cross Line". Well this has to be since Thrust is parallel to the Right Forearm's Angle of Approach, which is on the Inclined Plane. So it's Cross Line in the senese that the Thrust is pointing well to the right of your Target. This is true regardless of the origin of your Thrust – muscularly (Hitting) or centrifugally (Swinging) – because Inclined Plane is Inclined.

"Delivery Motion is On Line". The Motion Homer is referring to is the movement of the Clubshaft and Clubhead. Since we are using the Basic Plane Line, the Clubshaft is Tracing this line also, and the motion of the Clubhead agrees with this On Line procedure. Note that this would not be true if we considered the case where the Hitter is using their Angle of Approach Delivery Line procedure, because their Clubhead now covers the Angle of Approach derived from the original Plane Line, and this produces a Cross Line Motion of the Clubhead. However, as I've explained above, the word "Normally" at the start of the sentence rules this out.