The NFL has a veritable alphabet soup of injury lists that can be used for players in various circumstances. PUP, NFI, short-term IR/ designated to return (IR/DTR, if you will). Judging from the @BigBlueView Twitter feed and some of the comments here at BBV in the wake of New York Giants safety Nat Berhe announcing he will undergo surgery Friday for a hardened blood clot in his there is a lot of confusion over what each list means, and which players on the Giants are eligible for them. So, let's try to explain.
Physically Unable to Perform (PUP)
The PUP list is used for players who are physically unable to practice when training camp begins. If a player participates in a single training camp practice he is NOT eligible for the PUP list. A player on the PUP list does not count against the 90-man training camp roster.
A player on the PUP list can be removed and added to the roster at any point during training camp or the preseason. That occurs when a player is medically cleared to participate. If, however, that player is still on the PUP list when the regular season begins he is not eligible to return until after six (6) weeks of the regular season. After that six-week regular season period teams get a three-week window to decide whether to add a player to the 53-man roster, put him on injured reserve or release him.
A player who begins the regular season on the PUP list does not need an IR designation while he remains on that list. The only Giant currently on the Physically Unable to Perform list is offensive tackle Will Beatty, who suffered a torn pectoral muscle during OTAs.
Reserve/Injury -- Designated To Return (IR/DTR)
A player who was on the roster during training camp or the preseason and suffers a "major" injury can be placed on the Reserve/Injured list and "designated for return." NFL teams are allowed ONE (1) such designation per season. Here is the section of the NFL bylaws explaining what happens once a player is given the "Reserve/Injured -- Designated For Return" tag:
Such player is eligible to return to practice if he has been on Reserve/Injured for at least six weeks from the date he is placed on Reserve. He is eligible to return to the Active List if he has been on Reserve/Injured for at least eight weeks from the date he is placed on Reserve.
So, a player on short-term IR will miss at least the first eight games of the regular season.
If no player is given the "IR/Designated for Return" tag prior to Week 1, the tag can be applied to a player in-season.
A player like Berhe COULD be given the "IR/Designated for Return" tag. So, too, could any Giants player injured during the preseason who could play eventually but won't be ready Week 1.
Non-Football Injury (NFI)
This is the list the Giants could choose to put Jason Pierre-Paul on should he sign his franchise tag tender prior to the beginning of the regular season.
The NFI list is for players who sustain injuries or illnesses not related to football. The rules for activation mirror those of the PUP list. The major difference, and one of the big reasons Pierre-Paul has not signed his tender is staying away from the Giants, is that teams can choose not to pay players for regular-season weeks spent on NFI.