Sprint
My 4/C son plays Sprint. After his appointment he received a letter suggesting he might try out for Sprint during plebe summer. (If you don't receive such a letter, try out anyway.) He was targeted because he played four years in high school (2 varsity letters) and fit the weight requirement, which is currently 170 pounds on the Tuesday before a game. Actually it might be 172 pounds. There is some talk of raising the weight limit. There is also a minimum body fat requirement, so they aren't killing themselves in season.
My son's HS playing weight was 155 pounds. After baseball season he was probably 150 pounds on I Day. He used on of his summer phone calls to ask for his protein drink shaker because during Sprint tryouts he was down to 140 pounds. Now he's 168.
To walk on, just walk on during Plebe Summer. Last year 80-85 plebes started the tryout. 14 made the cut, including my son. (One more plebe was added later, after an upperclassman quit.) He absolutely loves it. Expect the hardest workouts of your life. Sprint is run by Marines and most players go into that service. I even have a cool pair of Navy Sprint workout shorts that are red with the Marine seal and gold lettered "Navy Sprint Football". It isn't subtle.
You will be in shape. My son maxed out his PRT just a few months after badly spraining his ankle in practice.
It is an intercollegiate varsity sport. They win. A lot. I'm fairly certain everyone on the team has high school experience. You have to really love football to make it through the grueling workout regimen. "4th quarters" every day, etc. Many of the players were all-District, all-State, etc. but are undersized for D1 football. It is a fast, athletic game. A lot of good football players get cut. This is not a JV team. Their star RB was offered a spot on the "big boy" football team, but elected to stay a part of the Sprint "brotherhood". (They held a vote as to whether he could return.) Unfortunately he blew out his knee in their first game and missed the season. Their first game was against Coppin State's club team, which is one of the best club teams on the East Coast and has no weight restrictions. 300 pound and above linemen. Total blowout. For Navy. (The only game they lost was to Army by 3 points. So according to my son, this was a lost season.)
Last year, he got to play at Cornell, Princeton, and Penn. Hours of uninterrupted sleep on a bus!