Redshirt

A redshirt is a college athlete who practices with the team but doesn't compete in games for a season, preserving a year of eligibility: He redshirted his freshman year to develop his skills.

The term comes from the red jerseys such players traditionally wore in scrimmages.

In science fiction fandom, a redshirt is a minor character destined to die—from the expendable crew members in red uniforms on the original *Star Trek*.