Restart SSH service via command-line?

I'm running LE on a RPi3 and I'm sending files to it via rsync over SSH. This all works.

However, sometimes when the transfer gets interrupted, rsync will not work until after a reboot. It starts fine from the far end, but just stays there and no files are created on the Pi. I've tried killing all rsync instances on the remote pi, but it doesn't help. I'd like to be able to get things going again, remotely over ssh, without a reboot if I can. Restarting sshd is my next guess but I haven't figured out how LE manages services. Any ideas about either of these?