Tanking in games only really matters in video games. Such games usually have an invisible hate or enmity mechanic that tells who the NPCs should be attacking. While not universal, games usually follow a certain formula: healing generates large amounts of enmity, followed by the highest damage dealer. Tank classes typically have abilities that generate high levels of enmity, making them priority number one to kill. They also typically have higher levels of health and/or defense than other classes, meaning they can eat more attacks than the healers and damage dealers.
Some games mix things up by painting their tank classes in different ways. The Warrior from FFXIV, for example, has less defense than other tanks, but has a high damage output and the ability to recover health based on damage dealt. They essentially tank by being the biggest threat in the room.
Mechanically, the Sith Juggernaut from SW:TOR served as a tank class. However, the inspiration for that class was Darth Vader, who was hardly one to let himself be hit, or one to just stand back and block.
If we're discussing semantics, "juggernaut" as a word does not convey the idea of a defensive fighter , but an offensive one . That doesn't mean a hypothetical Juggernaut spec couldn't work as a tank, but it would mostly be by building up a lot of hate. Genesys' Realms of Terrinoth actually has a talent that works like this called Challenge!, which adds boost to attacks targeting the character, but setback to attacks targeting their allies.