Rivalries are what make sports great—and MLB is loaded with teams and fans looking for blood.
MLB was founded in 1869, and at this point some teams have been beating up on each other for more than 100 years. The emotions felt by players and fans during a game increase the tension and animosity of a rivalry, and over time there ends up being nothing but pure hatred for one another.
To be honest, I am a purist when it comes to baseball. I don't like Interleague play and I don't consider the "cross-town rivals" to be rivals at all.
The Cubs have played the White Sox only 78 times, while the Yankees have played the Mets a mere 81 times. How does this make them great rivals? Being from the same city doesn't make two teams rivals—consistently fighting for a common goal does.
Here are the "true" 7 greatest rivalries in baseball: