Back in April of 2014, the Jacksonville Jaguars and transition-tagged center Alex Mack agreed to terms on a large deal that would bring the stud center to Jacksonville for $42 million. The Cleveland Browns matched the offer, keeping Mack in Cleveland. As noted in that NFL.com article by Marc Sessler, this was a no-brainer for the Browns. Mack is that good.
But part of that cost was allowing Mack the option to opt out of the contract before the start of the league year in 2016.