It’s by IP:

The maths is brutal. On a match day, blocking just 4 to 20 IP addresses knocked out more than 400,000 unrelated domains. The outage lasted as long as the game.

None of this is new in kind, only in scale. Courts across Europe have long ordered providers to block pirate sites. Spain runs one of the continent’s most aggressive regimes. What has changed is the plumbing. The web now runs on shared infrastructure, so a crude IP block is a shotgun, not a scalpel.