can you block a connected device from google fiber
In fact their router doesn't even give you tools to fake block him (like assigning him to an IP that wouldn't route on your network). Mostly you're screwed and Google Fiber is bad for anyone who doesn't want to use their lacking and vanilla implementation. You can't even go bridge mode so you'll just be stuck with a double NAT, put your own router behind theirs, shut off WiFi on the Google router, and then block by MAC on your own router.