I think the term "redshirting" leads to more confusion than any other concept. We all use the term, although it has no well-defined meaning, and we tend to think that a player who redshirts is in some special category.
But he isn't.
For the moment, I'll leave aside the possibilities of a hardship waiver, which includes certain instances of injury.
The NCAA eligibility rules don't use the term "redshirt" and aren't structured in a way that would make the term useful. For D1 (other divisions are similar), a player is allowed a maximum of 4 seasons of competition, and has a limit of 5 calendar years in which to compete. At the end of the season, the squad list is updated to show whether a player was in the lineup at any time during any intercollegiate game. If he was, he is deemed to have used a season of competition. If he wasn't, he didn't use a season of competition. There isn't any declaration in advance, and it doesn't matter why he didn't play. It could be because injury makes him ineffective, or the coach didn't find a reason to play him, or it was a conscious decision to not compete. Either he did or he didn't. Until the season is over, the NCAA has no interest in his playing status, and at no time do they care why he didn't compete, excepting hardship cases.
99+% of the male student body "redshirts" each year, because they didn't play, and their eligibility is affected exactly the same way as a team member who doesn't play--no season of competition was used. So redshirting is not in any way a special category. It's the fact that he is on the team that makes him different from the rest of the students.
If a player suffers a hardship (season ending injury, family financial emergency, etc.) that stops him from playing baseball, and the hardship occurs early in the season, then the player may be awarded a hardship waiver, and can be deemed to not have used a season of competition, even though he competed in the early part of the season.
Additionally, if a player suffers hardship which prevents him from competing in two separate seasons, he may also get a different waiver which permits him 6 years in which to complete his 4 seasons.
