Essentially, restructuring a deal involves the conversion of a portion of a player's salary into the form of a signing bonus. The cap hit from that bonus can be amortized over the length of the contract, which in turn lowers this year's cap number.
Why do teams restructure contracts?
Whenever a team finds itself short on cap flexibility and needs some space, the most effective short-term fix is to restructure its long-term contract. Some teams can cut or trade players, but contract restructures allow a franchise to keep its roster intact and simultaneously provide instant cap relief.
What does restructuring an NFL contract mean?
Restructures are common moves in the NFL, especially in this unprecedented year, but they do have a cost. When a restructure is done, a player converts a portion of his base salary into a signing bonus, which is then prorated over the remaining years on his contract.