The Tuck Rule

CT Saints Fan said

Because the point where the arm changes from bringing it back to throwing forward is an actual, visual change in direction -- from <-- to -->. However, the throwing motion is an arc. At what point in the arc has the intention changed from throwing to not throwing?

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Its been a long time since I took geometry, but I think that an arc that going away from the center will at some point come back towards the center - that is when it ceases to be a "forward" pass. And just as the NFL lets refs determine when the motion is going forward, they should also let them determine when that motion has ceased going forward.