NFL owners approved changes to two procedures for the 2021 season, one on the field and one off.
The on-field change is essentially a broad expansion of the prohibition of blocking below the waist on kicks and change-of-possession plays, making it apply to many other plays from scrimmage. The off-field change applies to how big rosters can be for each team to start training camp and in what manner those rosters are then trimmed to the regular-season limit.
The latter one will affect teams first. Each team will be allowed to take 90 players into training camp, which will start in the last week of July. Those rosters must then be trimmed to 85 players on August 17 and to 80 players on August 24, each of which are the Tuesday's following the first and second weeks of preseason games.
The final cut to 53 players for the regular season will take place on August 31, the Tuesday after the third and final round of preseason contests. For the Tampa Bay Buccaneers and Dallas Cowboys, who will meet in the NFL's 2021 Kickoff Game on Thursday, August 9, that will be nine days before their first regular-season game. For most teams, it will be 12 days before their opening contest. In contrast, the cut to 53 previously occurred on the Saturday of Labor Day weekend, eight days before the first Sunday of the season.
This revision returns the league to the system of multiple cut deadlines that it had used up through the 2017 season. For the past three seasons, teams had been held to only the one final deadline, though they could choose to start trimming the roster earlier than that. That allowed teams to hold on to many of its younger players long enough for them to play in the final preseason game. Even with the new system, each team can keep at least 80 players through the end of the preseason schedule.
The blocking below the waist prohibition now applies to all plays and is only allowed within the "tight end box." Basically, that's a rectangle of space that extends five yards downfield past the line of scrimmage and two yards outside of offensive tackles on each side of the line. Otherwise, that type of blocking is not allowed by offensive or defensive players and is subject to a 15-yard penalty. The change was clearly made to enhance player safety.