Mason hired Fitch and a new defensive coordinator after last season. Then he had at least seven players opt out, with eight others transferring this year. Linebacker Dmitri Moore opted out, then changed his mind before deciding to transfer after playing in a loss to then-No. 6 Florida.
Vanderbilt became the first SEC school to have a game postponed due to not having at least 53 scholarship players available; that happened before a road trip to Missouri scheduled for October. The Commodores also played two other games with the number of scholarship players in the 50s.
The most notable thing to happen this season for Vanderbilt came Saturday, when soccer goalkeeper Sarah Fuller became the first woman to play in a Power Five conference football game.
Mason leaves as the sixth-winningest coach in program history at 27-55.
Vanderbilt said the search for a new head coach will begin immediately.