There are many reasons a student-athlete may redshirt. A student-athlete may redshirt to gain a year of practice with the team prior to participating in competition. In college football, a student-athlete may redshirt to add size prior to participating since football tends to favor larger players. Since the college years coincide with the typical completion of physical maturity, using a year of eligibility in the fifth college year is generally more beneficial to the team and to the student-athlete's potential professional prospects than it is to use the same year of eligibility in the first college year. Players, especially in football, may redshirt to learn the team's play book since college teams run more complex and more plays generally than most high school teams. In other cases, a player may be granted a redshirt if he or she has participated in less than 10% of the season taking place in an academic year. This rule is most commonly exercised in the Football Championship Subdivision of football (formerly known as I-AA). Commonly, an athlete will redshirt the first year of college, if the athlete is redshirting at all.
There is also a medical redshirt that may be obtained to replace a season lost to injury. A medical redshirt, called a "medical hardship" by the NCAA, can be granted by the governing body for a season lost completely or almost completely to injury. A medical redshirt can allow a player to gain additional eligibility beyond the standard four academic calendar years. On rare occasions, a player may be allowed to play in his or her sixth year of college if he or she suffered a serious injury which kept him or her from playing for more than one season.
