So you have 'football' and now you're supposed to add 'football' ? I'm guessing you might mean 'futbol' or perhaps 'basketball'. It's hard to recommend what approach you should take without knowing more about what it means to 'add another sport'. In addition to your database, you probably have lots of pages that run queries on that database. If you change the structure of your existing tables, then a lot of those queries might have to change.
Replicating an entire database might be the easiest way to go. That way, you could copy your scripts to a new directory, change the database connect code to the new database, and then you'd have a new project entirely separate from the old one. If you must use the same database, you might copy all your tables and prefix them with 'sport2_' or something.
Sorry I can't be of more assistance, the question you ask is not an easy one to answer without more information. The bottom line is that you need to consider how your code works with your database.
