I had the same question, but natty's ESPN article notes that the Saints did something similar, so I guess this is permissible under league rules, as odd as that seems given that it appears to purely be a legal fiction to game the cap rules.This doesn't make any sense. Why would the league allow a contract that give the Patriots cap savings this year, but the final two years are just fiction because they automatically void themselves?
Edit: apparently this is actually quite common, particularly for QBs, despite it seeming like an obvious loophole. This Deadspin article from two years ago indicates that Foles, Tyrod Taylor and Ryan Fitzpatrick all had similar "voiding" deals at one time or another:
So in this instance, the Pats are basically just getting short-term relief for this year with the risk that if they can't renegotiate by the end of this league year the pro-rated portion of Brady's signing bonus will hit their 2020 cap all at once. Of course, there is only so long the Pats will be able to play this game - if Brady decided to retire after this year, for example (not that that seems likely), the Pats' cap would be screwed for next year.What’s the point of the void language? Why not just make it a two-year deal? Because it buys the Eagles short-term cap relief. As of today, the Eagles have slightly less than $10 million in cap space, per NFLPA records. Foles’s deal was structured so he will count just $1.6 million against this year’s cap, and $7.6 million next year. He received a $3 million signing bonus that will be pro-rated at $600,000 per year across the five-year max life of the contract. And when the deal voids in 2019, his $1.8 million in remaining bonus proration will accelerate to the Eagles’ 2019 cap.
The void date also creates a deadline for a potential renegotiation. If the Eagles want to keep him, they have the chance to try to work out an extension while Foles is still under contract, before has a chance to bargain with other teams. And if they don’t want to bring him back, they can let the void kick in and eat the dead money, which by then might be more manageable for them to do, cap-wise.
Foles isn’t the only player with years on his contract that are completely ephemeral. The Bills similarly bought themselves immediate cap relief with Tyrod Taylor’s new five-year deal that automatically voids itself after two years. And last summer, the Jets had done something similar (albeit with a two-year structure) when they finally ended the saddest contract standoff in league history with Ryan Fitzpatrick.