Seems a German company is developing a system that would sense when a player is in an offsides position: http://sports.yahoo.com/m/sow/news/ap/20020925/ap-offsidescomputer.html At a quarter-million a pop, you're not gonna see these on every field any time soon, but if adopted, I'd expect the price to drop significantly. German refs seem somewhat warm to the idea. Rumors that the system will be called the "Roger Itaya 2000" haven't been confirmed...
Man, how does it tell when the ball is released? If it has any kind of acceleration detection device (for determining when it's struck), how would it know when it's played by the attacking team vs. deflected by the defense. Those are just SOME of my initial questions. By the way I was involved in some motion / location detection research writing the software for such things when I was in college, so that's the basis for some of my questions.