The Pittsburgh Steelers have a hard-and-fast policy about ending negotiating on contract extensions once the regular season begins, though they have made exceptions to other precedents in the very recent past. Those exceptions, though are few and far between; it has been many, many years since they last negotiated a contract with a player on their roster in-season.
This is not the norm around the rest of the NFL. In fact, it’s quite common within the AFC North, with the Baltimore Ravens especially prone to doing it. This year, it’s the Cleveland Browns, who have been busy this week trying to shore up their offensive line for the long term.