I could not get it to work with safari on a mac and emailed ESPN (answer below). I did download Firefox and it works great even full screen. Now I have to figure out how to link it to my flatscreen tv.
Hello,

I apologize for the frustration.

The Move Media Player is not currently compatible with the Snow Leopard OS and default Safari browser settings. You will be able to view the player if you switch to a Firefox browser or run Safari in 32 bit mode.

To change Safari to run in 32-bit mode do the following:
1) Open the Finder
2) Navigate to the Applications folder
3) Select Safari
4) GetInfo on Safari. (Done by Right Click/CTRL+CLICK and selecting GetInfo, through the File Menu, or CMD+I)
5) Select (enable/check) the checkbox for “Open in 32-bit mode”
6) Close the Safari Info window
7) Restart your Mac