He won't have to sit out a year.
As forensicbuzz said, unless he graduates, he will have to sit out a year. If he doesn't graduate, he still has a redshirt year, so he could sit out and play in two years. However, if he was planning to sit out a year, why go the FCS at all? The NCAA wording is shown below. If you tansfer to a D1 baseball, basketball, ice hockey, or FBS football you do not qualify for the one-time transfer exception. Marshal has already transferred and used this one-time exception, so he wouldn't be eligible for it even if he transferred to another FCS school.
One-time transfer exception: If you transfer from a four-year school, you may be immediately eligible to compete at your new school if you meet ALL the following conditions:
- You are transferring to a Division II or III school, or you are transferring to a Division I school in any sport other than baseball, men's or women's basketball, football (Football Bowl Subdivision) or men’s ice hockey. If you are transferring to a Division I school for any of the previously-listed sports, you may be eligible to compete immediately if you were not recruited by your original school and you have never received an athletics scholarship.
- You are academically and athletically eligible at your previous four-year school.
- You receive a transfer-release agreement from your previous four-year school.
Waiver: An action that sets aside an NCAA rule because a specific, extraordinary circumstance prevents you from meeting the rule. An NCAA school may file a waiver on your behalf; you cannot file a waiver for yourself. The school does not administer the waiver, the conference office or NCAA does.