Most football fans know that NFL teams suit up 46 players on game day while a club carries 53 players on its active roster. Many have asked why have extra players that can’t be used. After all, there is a 10-man practice squad as well.
Some have suggested that all 53 players be allowed to dress and play. On the surface, limiting players to 46 seems capricious, but there is actually logic to the rule.
In order to understand the reasoning, one must first understand the NFL rules for injured reserve. Unlike other leagues, injured reserve is essentially a one-way street from which there is no return. For example in baseball, there is a 15 and 60 day disabled list, which amounts to temporary and reversible injured reserve. In 2012, the NFL allowed one player on injured reserve to be “designated for return” after a minimum of eight weeks.
In order to qualify for injured reserve, an active roster player must be considered to suffer a significant injury lasting at least six weeks. In other words, a player with a mild ankle sprain does not qualify for injured reserve. Minor injuries are expected to be carried on the active roster. Along with strategic decisions, that is the reason for not allowing all players to suit up for games.
As the season starts, the term physically unable to perform (PUP) will be used. PUP is used for players that begin the season injured and can’t pass a physical. It gives players time to get healthy while allowing teams to use the roster spot. If placed on PUP, a player may not return until week six. If they are not activated by week 12, then they need to be moved to injured reserve.
Some have called for all players to be active on Sunday. On the surface, this seems to be a good idea. After all, all 53 are being paid and count against the salary cap. A new rule allowing all to play would push teams to place injured athletes to injured reserve instead of carrying them on the active roster in order to avoid being at a disadvantage. A club with a number of injured players could be playing shorthanded compared to a healthy team.
In 2012, the new category of IR-designated to return began. After the season starts, each team can name one player that potentially could be brought back off of IR after week eight. The idea is if a player suffers a serious injury early in the season, he could still return if he can get healthy and a team could utilize the roster spot in the meantime.
My understanding is that in the past, teams would stockpile players by placing them on injured reserve. It is a given that football produces injuries. One main reason for a 53-man roster but only suiting up 46 is to allow for injuries. If there really is a change to allow all players to suit up, the NFL would have to create better short term IR options
Dr. David Chao  wrote: