Not as daft as it sounds;
I’ve spent a large part of my life over the last 2 years working on tracking systems. And the technology to do this already exists, it has for about the past 5 years.
I haven’t fully thought this through but off the top of my head.
You would need a grid of receivers, achieved by installing a small device along one side and end of the pitch every metre; these are about half the size of a mobile phone and can be housed in weather proof enclosures, most grounds could accommodate these along the eves of the stands.
Each player would have a transmitter installed in their boots, anywhere else would not work, e.g. wristbands, players would soon learn to make a run with a trailing arm.
The code base from any for the current key tracer, employee tracker or door entry systems could be altered in a couple of months.
The ball would need an impact transmitter.
A system of this type is capable of taking 20 readings per second so would be accurate to how far a player can move in 1/20th of a second. This could be factored into the software as an error margin.
The system works by triangulating a ping sent from the players boots so is not reliant on GPS or any third party system.
That’s about it but what would it do.
At the start of a match each player would have to stand on a pad set at known co-ordinates which would read the players chip and configure their boots and current position, this could just be a mat rolled out at the end of the tunnel that the players run over.
A similar reader could also be placed in the plinth where the ball sits before kick off.
The position of every players feet and the ball would then be visible on a screen in real time, not the actual match, a grid with dots representing boots and ball. this could be anywhere in the world.
For any possible off side the system would know the position of every players feet at the moment the ball was played.
I can see some limitations, the system would know the moment the ball was played but not who played it, but isn’t that the referees job.
The system could only read when the ball was kicked, headed etc, but the current off side rule states when the ball leaves the player, there is a time difference between a players foot contacting the ball and the ball leaving a players foot during a pass, is that time difference significant.
Advantages:
Accuracy not dependant on frame rates.
No blurry images.
No made up lines all over the pitch.
Ref and linesmen decide if its offside or not and use the technology to assist in close calls.
Would take 10 seconds to look at the screen.
Disadvantages:
These systems are proven technology, they work, they are simple and they are secure. This could be implemented in every Premier League ground for about a million quid. The Premier League would want to spend 500 million, redesign the hardware, rewrite the software from scratch, take 5 years and make a complete bollocks of the whole thing.