The thing I always get with video technology in football is where do you draw the line? What things can be challenged.
Say you have someone run free on goal, and gets called offside when he isn't. He doesn't shoot, doesn't score, he gets pulled back before he can. Does that get a video decision? Whats the point of it though the opportunity has gone, all advantage is gone, you can't decide it's a goal, so what do you do? Call it a free kick which is less advantageous? Is it worth it in that matter?
If video refs are going to work, it can only be for goals, pens, and blatant red cards. Thats it. Anything else is either too subjective or does not stem from a moment when play stops sufficiently.
To add to that point, you have to make sure games aren't bogged down by multiple 4 minute breaks; sure you can say you can add the time on later, but football more than Rugby and Cricket is a momentum sport. If you have a team on the ropes a 4 minute break is a killer for you. We should know that better than anyone our whole game is built around constant preassure which forces mistakes and panic states, this type of stoppage would hurt our football badly as it allows the opposition to regroup and catch their breath.
For me, goal decisions can be made with a video ref easily; ball goes in, play stops, ref calls for an opinion, or the video ref watches a replay independently and if needs be counters the refs decision.
Red cards seem easy too; if a particularly violent incident occurs and the ref doesn't see it, video ref can watch, and inform the ref to send the player off the next break in play.
Penalties seem a lot harder; many times a foul can haplen in the box and play doesn't stop. I can only see a penalty decision working on appeals. As someone said, it isn't fair dragging play back for a pen from the other end of the feild 2 minutes after the incident; not only does this make the opposition conceed the pen, but also lose out on a goal scoring opportunity they made completely seperately; it's being punished twice. Pens I therefore think will only work by appealing to the ref after the incident and forcing him to stop play to check. Obviously, there will have to be a set number of appeals so that teams can't abuse it to disrupt play.
For incorrect referee decisions, again play usually stops so these can be easily checked, but the difficulty here is they can be subjective (a penalty incorrectly given in one mans eyes may be correct in anothers. Same with Red Cards; just yesterday people were arguing on the radio over whether Vardy deserved a red or not)
