Quote: SmokeyTA "Im not proposing Hawkeye, im saying Hawkeye as a system, which whilst not infallible is less fallible than the human eye, can judge a much more complex rule such as LBW then there should be no problem with a system which can judge forward passes.'"
LBW would be considerably less complicated. A cricket ball will only travel at most 2 metres up and down, 1 metre side to side, and the 22 yards along the pitch. The Hawkeye cameras have to only watch a small volume, while some computers can then calculate the trajectories and where the ball would most likely end up had it not hit the leg pad.
In rugby you would have to increase the volume that hawkeye-style cameras must watch by a factor of a thousand. And then it would have to figure out loads of other things like how fast the player was moving when he passed it, the exact moment of the passing action, whether wind affected the ball after it was inflight, in what direction the player was passing it...
Doing all this while the cameras probably can't even see the ball due to the mass of players around it would make it a tough job. I'm not saying it's impossible, but I don't think the specific technology currently exists to do this as accurately as is wanted by most spectators. Or at least it would be hugely financially unviable.