When a professional football player introduces himself and states his college affiliation, must that player have graduated from that college or does 3 years allow for him to declare that school affiliation? Some players note a HS affiliation; If they mention a HS, does that mean they did not attend college?
There are no rules. Players get to give a shout out to one school and they say whatever they want. Would the networks let a player who went to Miami say they went to Oregon? Probably not. But as long as a player played at a school they can mention that school.
Some players mention their high school out of pride, others have done it because they left on bad terms with their college and don't want to mention them, and some go back and forth saying their high school sometimes and their college sometimes.
If a player says which high school they went to I wouldn't read into that at all since 99%+ attended some college to play football at some point - it might not be D-I and could even be community college but there are very very players in the NFL that didn't play in college (I know a few foreign born kickers and a couple rugby players).
The other note is that players have pretty much a free rein on how they say the name of their college. The word "THE" has been added to the name of many colleges to, I guess, gain more respect. The whole naming of your school is just a fun thing that a player gets to do for each game. These are usually done the day before and fresh for NFL games. They also need to get 11 guys to say their college in between a play - about 40 seconds. So it is quite funny watching guys try to say the name of their college as slow as possible.
Note: Was discussing this with another buddy that watches almost every game... We both remember (or possibly misremember) at least one shout out to a junior high and to a peewee team or coach. If anyone has proof please add it to the comments.
As others have noted, there are no real requirements on this. Most players specify their college, though in recent years some have begun calling out their high school.
One more complicated situation is when a player transferred part way through their college career. For example, Russell Wilson began his collegiate career at North Carolina State (Mascot is the Wolfpack). Then, after completing his undergraduate degree, he attended the University of Wisconsin (Mascot is the Badgers) for grad school and played for them. Most players would choose one college or the other to shout out (most likely the most recent school). Russell Wilson has chosen to try to incorporate both schools by introducing himself as
Russell Wilson, from a whole Pack of Badgers.
A professional football player gives the last school where he had "trained," before joining a professional team.
More often than not, that means a college. And he may or may not have graduated (many football players attend college for the chance to "play," rather than for the education, and leave as soon as a team will sign them, that is, after three years). Sometimes, it could refer to a player that attended college for five years, but was "red shirted" by the team for one year. (That means that the player was put through an extra year of training but was technically not a member of the team because he was not allowed to play for that year, and therefore only played for "four.")
If a player joined the team out of a high school, with no college "education," he will use the high school as his affiliation.