Managing NFL rosters has turned into a real balancing act for general managers. With the constant flow of injuries and player evaluations, it’s like a game of musical chairs trying to keep the roster at its peak. Teams start with a hefty 90 players during training camp, and after grueling practices, only 53 make it to the regular season. But the roster shuffling doesn’t end there.

Players can be placed on different lists depending on their injuries and recovery status. One of these is the Injured Reserve (IR) list. “Players on IR are sidelined for at least a few weeks due to injury and don’t count against the active roster,” the league’s guidelines explain.

If they’re on IR before the season starts, they could be out for the entire year unless they’re designated to return. This year, teams can have up to two players designated for return from IR, with a minimum of four games they need to miss. Once a player is cleared to practice, they have a 21-day window to be activated or put on season-ending IR.

What exactly is the PUP?

Then there’s the Physically Unable to Perform (PUP) list. Players on the active/PUP list at the start of training camp have injuries but can still participate in team activities. They can be activated at any time, provided they’re medically cleared. However, players can’t be placed on the PUP list after they’ve practiced or played in a preseason game. If a player is on the reserve/PUP list, they’re not counted towards the 53-man roster and must sit out the first four games of the season. “A player on Reserve/PUP can practice and rejoin the team after six weeks, but they must be activated within 21 days,” the league’s rulebook states.

The Reserve/PUP list is crucial for managing injuries. “Players on Reserve/PUP can’t practice or play during the first six weeks, but they’re eligible to return after that,” notes a 2013 ESPN blog post by Mike Sando. After the six-week period, players have a 21-day window to be activated or put on the inactive list.

For example, Jonathan Stewart of the Carolina Panthers, who had offseason surgery on both ankles, will miss the first six weeks of the season. Meanwhile, players like Michael Crabtree, who tore his Achilles, are on the Reserve/PUP list and won’t return until at least Week 11. And while Ed Reed was on the Active/PUP list with a hip injury, his status was re-evaluated by the end of August.

Overall, while no player wants to land on these lists, understanding their purpose and impact is key to navigating the NFL season.