Is there by any chance a RealPlayer shortcut button somewhere close to your location bar? It's easy enough accidentally to hit such a thing after typing in a new URL.

You don't say what version of Real you are using, but as a rule my general advice would be the same for all; go into 'Preferences' and turn off every function you can except the association with Real's native media.

Then, if you still need to, take Jeri's advice; but always try the simple things first.