This question already has an answer here:
Imagine the following completely hypothetical scenario:
I have Chris Davis on my team (I am Dan Duquette). I know that Chris will be a free agent next year, and I want to keep him. I sign him to a multi-year deal that goes into effect next season - and doesn't begin until then.
At the trading deadline; realizing I will not compete, I trade him to the Diamondbacks for Ken Griffey the Third, Alex Rodriguez's cousin, and a genetic clone of Pedro Martinez.
I do this knowing that next season Chris will be back, and The Orioles now have murderers row.
When the next season starts Chris's contract kicks in and he's an Oriole again.
I'm sure that this is illegal, but I can't find any mention of it on Google. Does anyone know the rules (if any) referencing this type of situation?