Expanding on Mark B's cooment......
A D1 player elibility expires 5 calendar years after enrolling full time in any college.
He also is limited to a maximum of 4 seasons of competition.
Waivers:
1) If the player has competed-- thus using a season of comptition-- but suffers some hardship fairly early in the season which ends his season, he may be granted a hardship waiver which will permit him a 5th season of competition. Hardship could include injury, physical illness, mental illness, family financial catastrophe, etc. Typically, injuries which happen before the season begins don't require a waiver, because the player hasn't competed, and so doesn't use a season of competition. It doesn't matter whether the injury or hardship is related to or caused by baseball.
2) If the player has two seasons interrupted by hardship, he may be granted a waiver permitting a 6th calendar year.
So in this case:
Year 1 no competition [4 years left, 4 seasons left]
Year 2 competes [3 years left, 3 seasons left]
Year 3 no competition [2 years left, 3 seasons left]
Year 4 assume competition [1 years left, 2 seasons left]
Year 5 assume 2nd hardship [0 years left, 2 seasons left], but if waiver is granted,[1 years left, 2 seasons left]
The result of the player redshirting during his freshman (or other) year is that he runs out of calendar time before he runs out of seasons of competion, if he also has a season-ending injury.