An NFL roster consists of 53 players. 11 players are allowed on the field at one time, per team; either for offense or defense. Of the 53-man roster, on 46 with be suited up for the game. Each team can carry a little bit on how many players they have for each offensive and defensive position. It all depends on the type of offense and defense a team plays. If a team chooses to use a 3-4 defense then they will keep more linebackers on the roster.
Most teams will have 2 quarterbacks suited up for the game, but have an emergency 3rd quarterback on the roster. Sometimes the emergency quarterback is a running back or a wide receiver, but not always. Lets take a look at a 53-man roster with a 4-3 base defense team.
Running Back: many teams will employ 4 running backs on the roster. There is a fairly large history of injury in this position, that is why they have 4 on the roster and not any less.
Wide Receiver: most teams elect to have 6 on the roster, and 5 of them will be in uniform on game day. They will have the 6th suited up if he is an asset on the “special teams”.
Special teams is a unit on the field during the kicking plays. Special teams handles; kick offs, punts, and punt returns. There are 21 players on the field during a punt; kickers, punter, long-snapper and a group involved in return coverage. Normally the faster more skilled runners on the team will be in the back field to catch and run the ball.
Tight Ends: normally 3 on ever teams roster. You have the starting tight end, the back up (who usually is a blocking tight end), and a “hybrid” who also helps on special teams.
Offensive Linemen: there are 9 on the roster, though most coaches would love to have 10. Having talented and versatile linemen is key on a team to be successful. Most can play center if needed and right tackle can switch to left at the drop of a hat and visa versa.
So, on the offensive side of the ball you have 24 players on the 53-man roster. 21 will be in uniform on game day; 2 quarterbacks, 4 running backs, 7 offensive linemen, 3 tight ends, and 5 wide receivers.
On the defensive side, the 53-man roster has 26 defensive players, with 22 of them ready to be on the field on game day. 8 defensive linemen, 7 linebackers, and 7 defensive backs. The defensive backs are broke down into other defensive positions, such as safeties and cornerback.
Defensive Lineman: 9 defensive linemen are on the roster. On the defensive front you will have a 2 deep roster. Some teams opt to keep a designated pass rusher on the roster. Again, it all depends on the base defense team and the injuries before game day.
Linebacker: the majority of teams employ 7 linebackers on the 53-man roster. The core of the special teams, comes from the linebackers. Most teams will only have 3 on the field while they are playing defense.
Defensive backs: 10 defensive backs with 7 or 8 suited up on game day. Normally you have 4 corner backs and 2 safeties, but sometimes teams will do 3 corner backs with an extra safety on the field.
To round out the 53-man roster; add in one kicker, the punter and the long snapper and you have yourself a complete football team.
Now we all have a little bit better understanding and insight on what the front office personnel and coaches work on year round. They have to tweak the roster based on depth and ability of the players and of course they have to take the salary cap into consideration. They are consistently looking at film, stats, and overall health of the players during the season and in the off season, before the draft.