Knowledge about a subject enables you to establish what is likely to happen in future.
Knowledge about what
subject? How to hit a tennis ball? What the results of past tennis matches are? How to report on a match effectively?
The best evidence of expertise is proof that a person is widely recognized as a expert.
An expert on what? I'm sure Sampras is widely regarded as an expert on hitting awkward volleys and making booming first serves. Does that mean he can tell us what the top 10 will be 5 years from now?