Quote Horatio Yed="Horatio Yed"So i'm assuming if the wingers velocity is slower it's easy to judge but if its faster then it becomes more complicated?'"
Sort of.
It's the player who passed the ball who's speed is important the faster he is going the faster the ball is traveling forward too. So a pass he makes, even if he passes the ball backwards relative to him, may travel forward relative to the pitch, this is not a forward pass though. The faster the player is moving forward, the faster the ball is traveling forward relative to the pitch, and the effect will be more exaggerated. It also looks worse on a long pass as everyone in the ground can clearly see the ball travel forwards, relative to the pitch, and can become very frustrated when what looks a clear forward pass is not given. You are correct in thinking that the speed makes it more difficult to judge. Most forward passes are given from acting half, when the player passing is moving sideways or is stationary, those are easy to spot.
Bringing in the player who catches the ball complicates the issue. It's two players relative speed and positions that could be used to judge whether the ball has gone forward or not. The absolute speed of each player is not the issue.
If you imagine two players on a breakaway running flat out at say 10m/s. Then the ball is travelling at this speed too. Now lets say player A passes the ball to player B who is 1m behind him, relative to the try line. Even if the ball is in the air for 0.5 seconds it will travel forward 4m relative to the pitch. This will not be a forward pass and will look fine if player A continues to run forward. If player A stops though (gets smashed as he passes) it will look a mile forward and the crowd will be incensed. If both players were running at the same speed, then you could use player B's position when he catches the ball to assume where player A would be had he not been smashed.
A good rule of thumb, is that if two players are running flat out, and the receiving player is behind the passing player when the ball is released, then it's not a forward pass. Even if it goes forward, the ref's don't generally give them.
On a related note, the ref is often in the worst possible position to judge whether a pass has gone forward or not.