You have the $50M in your pocket which would have made you rich, but now you owe $300 to the Yankees, because the Cubs have defaulted.
That wasn't an analogy, it was a derivative.
A better analogy would be that someone set up a trading company to swap the market value of sports clubs to provide insurance against the drop in the club's value created by winning and losing baseball games.
Okay. let's examine your idea.
The Cubs increasing in value by $300M would offset the Yankees dropping $300M . What if the cubs go into bankruptcy and cannot pay the $300M they owe, and which you owe the Yankees.
Back up. Who is buying this insurance? Who is selling?