What is the difference between a regular trade and a companion trade in baseball?
The term "companion trade" is being bandied about now with the impending trade of Roy Halladay from the Blue Jays to the Phillies. If the Phillies land Halladay, who is in the final year of his contract and will command huge dollars in his next contract, the Phils will have to part with Cliff Lee whose contract has expired and also will command huge dollars. There is no way the Phillies can sign them both and be under the Luxury Tax threshold for 2010.
So once the Phils get Halladay, they will trade Lee. Both trades are 'regular trades' but the Lee trade is called a 'companion trade' because it is being done because of the Phils trading for Halladay. It is kind of like the logic "IF A THEN B" with A being the Phils getting Halliday in a trade and B being the Phils will trade Lee.
The word companion could be defined as "something that accompanies or assists something else". The Lee trade will accompany the Halladay trade.