In college football, what is the definition of a redshirt freshman and a true freshman?
When a freshman athlete is referred to as being "true," it means that freshman is playing for the school during his or her first year of college classes.
When a player is given the "red-shirt" designation by his or her coach, that means he or she has participated in a college's academic year, but did not participate during that year's sports season.
Most likely a "red-shirt freshman" in college football is a sophomore in college who practiced with the team his first year, but did not play in any games (at the coach's request), or was seriously injured during his first season. The "red-shirt" designation means that that season will not count against the player's four years of NCAA eligibility, allowing him to play four full seasons.
—The Fact Monster