While there has been a fair amount of technical progress in concert and show tickets, sports tickets haven't quite made that leap yet: they're still either partly analog (read: old-school paper) or tend to be limited to a narrow group of sellers. NFL and Ticketmaster are hoping to fix that. They're extending their partnership to create what they say is the first open, all-digital ticketing system for sports. It'll both modernize the ticket process with less chance of fraud or other security woes, but will validate tickets at other sites. You can go through a third party knowing their tickets are the real deal and aren't coming from scalpers.
This will still allow for ticket trades, and season ticket holders can resell directly through the account manager.
This isn't mandatory; Ticketmaster will be the "preferred" primary ticket partner when the pact kicks in during the 2018-2019 season. However, it's likely that teams and stadiums will push this. It could cut back on scams and scalpers, but it also makes ticket purchases relatively easy to track. The league will have a sense of who's attending, where tickets are being traded and otherwise get a better feel for who their audience is. You could see the NFL change its marketing strategy to better target those most likely to buy.