Where is the flight into SFO from? If international, you will pick up luggage at SFO and clear customs, so you can just leave the airport and skip the Monterey flight. Nothing will happen, just leave SFO.

With an 8 hour layover, you might convince them to allow you to just check your bags only to SFO, since you will need your bags for the layover.

There's no 'splainin' the wackiness of certain airfares.

And you might enjoy visiting Monterey, anyway.

Welcome to FT!