Redshirted

Redshirt, in United States college athletics, is a delay or suspension of an athlete's participation in order to lengthen his or her period of eligibility. Typically, a student's athletic eligibility in a given sport is four seasons, a number derived from the four years of academic classes that are normally required to obtain a bachelor's degree at an American college or university. However, in a redshirt year, student athletes may attend classes at the college or university, practice with an athletic team, and dress for play but may not compete in games. Using this mechanism, a student athlete has up to five academic years to use the four years of eligibility, thus becoming a fifth-year senior.

The origin of the term redshirt was likely from Warren Alfson of the University of Nebraska who, in 1937, asked to practice but not play and wore a Nebraska redshirt without a number. The term is used as a verb, noun, and adjective. For example, a coach may choose to redshirt a player who is then referred to as a redshirt, and a redshirt freshman refers to an athlete in the first year of eligibility.

Student athletes become redshirts for many reasons. One reason is that the athlete may not be ready to balance the demands of academic requirements with athletic requirements. Redshirting provides the opportunity, with tutoring, to take some classes and get accustomed to the academic demands. They also 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 increase size and strength toward the completion of overall physical maturity, desirable assets for many positions. As the college years coincide with the final phases of physical maturity, using a year of eligibility in the last 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 typically run a greater number of, and more complex, plays than most high school teams.

...
Wikipedia