Sprint Geezer,
I am far from an expert on CAS, but it is an international tribunal to settle disputes. It has binding arbitration agreements with the IOC and IAAF that have been upheld in courts in a number of international jurisdictions. It also has agreements w/ many national oranizing bodies, including the USATF. I believe courts in the US have refused to get involved or overturn some decisions, leaving them to the CAS to be resolved.