What’s the definition of a rival? According to the dictionary, it’s this:
a person or thing that tries to defeat or be more successful than another
something or someone that is as good or almost as good as another person or thing
Applying the first definition, the relationship between Serena Williams and Maria Sharapova is a rivalry. The game’s fiercest fighters and biggest earners, who make no secret of the fact they don’t really like each other, have been in direct competition for tennis’s top prizes for over a decade, and are facing each other for a 20th time today.