mdhsbbfan,
You might want to mention the division you are asking about (DI, DII, NAIA) to help people give you a specific answer, BUT ... I think the answer is that at the levels which permit redshirting, one at-bat or field appearance in one game makes the redshirt unavailable for that year. Medical hardship/injury is a different story - that one depends on date and # of innings played.