@TigerSJ said in [Hawkeye for forward passes?](/post/1042171) said:
As I remember it, a fundamental rule of the game growing up was simply that your team mate needed to be behind you and you threw the ball backwards
I'm not saying this would not work, however I think you mis-remember the rule. I am pretty sure that it's always been about throwing the ball in a backwards motion, not whether or not the catcher is strictly standing behind the line where you threw it from.
I am of the opinion that introducing a strict definition of a forward pass as you suggest, albeit easy to understand and theoretically reasonable to adjudicate on video, will drastically increase the number of passes that are called forward.
For instance, I would imagine that pretty much every line break that results in a try will be called back, because sprinting players who throw backwards passes are still travelling at such a velocity that the ball will technically move forwards relative to the flat plane of the ground.
Case in point - you only need to go back to last round, the Luke Brooks break to set up Corey Thompson. Both frames are taken from the same camera angle and same replay, so there's no change in scale. First frame I took a distance measurement in red, second frame I copied that distance measurement down to the line that Corey is running.
Before:

After:

By your rule that is a forward pass by about one metre. However watch the replay and there is absolutely no suggestion of a forward pass.