Researchers in soccer-obssesed Germany are working on putting RFID tags actually into soccer balls themselves and into players' clothes:
A prototype has been developed in cooperation with the Fraunhofer Institute for Integrated Circuits, Erlangen. Once the system is fully functional, it could not only be of help to referees, but also deliver all kinds of interesting data for TV and useful information to the coach since every player could also be equipped with a broadcasting chip. This way, all players' paths, accelarations and speeds could be tracked in real time and converted into graphics.
This info might be more useful to coaches and opponents than to fans -- if it's really useful at all to know that Becks slows his approach by 18% in the final 10 minutes of a match, unless being pursued by a halfback if the ball is past midfield...
Still, it's damn cool that 1) RFID (and Wifi!) are not just used for communications and product tracking but for new applications and 2) it's not all GPS anymore (which was kind of limited for this kind of thing -- domed stadiums, slow locks...)
Other sporting ideas off the top of my head:
Baseball -- end speculation about how far that ball went, find out how fast your favorite slugger swings...
Football -- did the ball really cross the plane of the endzone?
NASCAR -- more stats about driving in circles
But the real advantage may be metrics not yet dreamt up. Footballoutsiders.com tries to take new stats about teams to predict victories, but RFID might open up new stats like "percent of players who run faster than 14 mph on more than 50% of plays" or "team with greatest linebacker kinetic energy".