On Sunday, the New England Patriots agreed to a contract extension through 2021 with legendary quarterback Tom Brady, but there is a bit of a catch: due to a provision that does not allow the Patriots to franchise or transition tag Brady after this coming season, he will actually be a free agent next offseason, according to Ian Rapoport of NFL Network.

Obviously, that's confusing, but essentially, the 2020 and 2021 years on Brady's new deal are void years, so if he is still on the roster come March 18, the deal gets voided. If the Patriots release him, New England can't apply a tag to keep him for the following season.

So, why would the Pats and Brady even agree to this deal, then?

Well, as part of the deal, Brady will get an $8 million raise in 2019, and the Patriots will also open up some cap room for the future as a result.

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But let's be honest here: none of this really means all that much, as it would be beyond shocking if Brady played anywhere else other than New England, so he will almost certainly finish his career out with the Pats before retiring.

The 42-year-old is coming off of a 2018 campaign in which he threw for 4,355 yards, 29 touchdowns and 11 interceptions while completing 65.8 percent of his passes and posting a passer rating of 97.7 en route to a Pro Bowl appearance.

Brady then went on to lead the Patriots to their sixth Super Bowl championship in spite of some second-half struggles that had some wondering whether or not the future Hall-of-Famer was finally in decline.