This sort of thing is relatively common in Britain.

After the riots in 2011, several people were arrested and jailed, some for fairly lengthy periods (years) for posting that they were going to start rioting in various towns.

Most didn't actually get involved in the physical confrontation or violence, or even leave their houses, but were charged with "incitement."

There have been similar cases since for less serious matters, particularly when it comes to messages posted on Twitter. I don't recall all the details, but someone was arrested for "threatening" an Olympic diver on the site a few weeks ago.

It's sad that this news story doesn't even shock me. It's so common here now. (Mind you, this lad looks like he'd be safer off the roads.)