Williams is coming off a terrific season in New York, during which he set career highs in sacks (11.5), tackles for loss (14), and quarterback hits (30). He's 26 years old (turning 27 in June) and about to enter his physical prime. He'll presumably be sought after on the open market -- if he gets there.
Williams played last season on the franchise tag, with the Giants paying him around $16.1 million. The team can use the franchise tag on Williams for a second time, which would necessitate a 20 percent raise, to $19.4 million, fully guaranteed for the 2021 season.
But Williams has filed a grievance with the NFLPA over his tag number. He wants to be classified as a defensive end rather than a defensive tackle. If he wins, according to ESPN's Jeremy Fowler, his 2020 tag number would shoot up from $16.1 million to $17.8 million, which means a second tag would earn him $21.4 million instead of $19.4 million. Overall, the distinction is thus worth around $3.8 million to Williams.
Williams seemingly has a pretty good argument to be classified as a defensive end. According to Pro Football Focus, Williams played only 369 of his 800 defensive snaps at defensive tackle last season, which means he spent more time playing as an end. The grievance remains unresolved at the moment, though, per Fowler, and that creates some uncertainty for both Williams and the Giants in contract negotiations this offseason. Classification as a defensive end gives Williams a higher starting point for his salary, which obviously affects the value of a long-term deal.