The Fraunhofer Institute for Integrated Circuits in Germany (yes, the MP3 and AAC people) is working on an RFID system for soccer balls and jerseys. The chip embedded in the ball has been worked down to the size of a fingernail. The biggest problem right now is suspending the chip in the middle of the ball to measure acceleration and protect against being pummeled as part of the outer skin. An article in German is available here, or you can use Google for the English translation.
This technology would be a great coaching tool. Right now in pro soccer there is a person with a set of binoculars sitting next to a person with a laptop computer in a skybox. The observer notes who touched the ball and where, and the computer operator enters that data point. Very tedious and expensive. Now imagine detailed data on where your plays develop, the speed and acceleration of different players, and even the strength of an injury causing tackle. You could also track the ball’s trajectory and your player’s ability to handle a ball from different angles. Very cool.