Through 5 games of the 2020 season, the Pittsburgh Steelers ranked ninth in the NFL with 684 rushing yards, averaging 136.8 yards per game. The rest of the 2020 season the Steelers would rush for 667 yards, 60.6 yards per game, bad enough to finish the season ranked last in the NFL.
What happened? Two big things. First, the offensive line play declined with nagging injuries and age, and second, teams stopped respecting the Steelers deep passing game and started running single high safety against them, allowing them to have 1 more defender in the box than the Steelers had blockers.