I am a TCG judge, but there are also judges for the video game and Pokémon Go. I can only answer why the TCG has judges.
Sometimes, the rules present some ambiguity, so a judge is needed to resolve disputes. There are also niche edge cases which not all people are aware of (for example, you generally can’t play a card that searches your deck if you have no cards in your deck, unless the card has other effects), so it’s helpful to have a rules expert on hand.
Some tournaments have significant prizes on the line. I’ve reffed events where the total prize pool was hundreds of dollars. When that happens, inevitably, there are disputes and people make mistakes. Judges are there to enforce the tournament rules and serve as the official arbiters for disputes. Sometimes, people inadvertently break the rules, by playing cards they’re not supposed to or by forgetting to perform a required action. When that happens, a judge steps in to resolve. And sometimes, disputes are just petty adults acting like children, like complaining that your opponent did not shuffle their deck throroughly enough (but sometimes we do observe actual children not shuffling their deck well enough, but they’re children so we just go and shuffle for them)
Judges also deal with disciplinary problems too. For example, we have the ability to issue penalties to players for rules infractions or disqualify or ban them for being disruptive. These penalties are recorded on the Pokémon Company’s player database and if a player gets kicked out of too many events (especially prestigious ones like a regional tournament, North America/European Internationals, or the world championship), they eventually may be prevented from attending events.
It’s fortunately never happened at any event I’ve worked at, but an examples of some things that would get a player disqualified would be failing a deck legality check unless the player fixes it immediately, cursing excessively, annoying other players and refusing to stop when asked, being caught cheating, wearing inappropriate clothing/not exercising good personal hygiene, or drinking alcohol or being drunk/high.
I am a TCG judge, but there are also judges for the video game and Pokémon Go. I can only answer why the TCG has judges.
Sometimes, the rules present some ambiguity, so a judge is needed to resolve disputes. There are also niche edge cases which not all people are aware of (for example, you generally can’t play a card that searches your deck if you have no cards in your deck, unless the card has other effects), so it’s helpful to have a rules expert on hand.
Some tournaments have significant prizes on the line. I’ve reffed events where the total prize pool was hundreds of dollars. When that happens, inevitably, there are disputes and people make mistakes. Judges are there to enforce the tournament rules and serve as the official arbiters for disputes. Sometimes, people inadvertently break the rules, by playing cards they’re not supposed to or by forgetting to perform a required action. When that happens, a judge steps in to resolve. And sometimes, disputes are just petty adults acting like children, like complaining that your opponent did not shuffle their deck throroughly enough (but sometimes we do observe actual children not shuffling their deck well enough, but they’re children so we just go and shuffle for them)
Judges also deal with disciplinary problems too. For example, we have the ability to issue penalties to players for rules infractions or disqualify or ban them for being disruptive. These penalties are recorded on the Pokémon Company’s player database and if a player gets kicked out of too many events (especially prestigious ones like a regional tournament, North America/European Internationals, or the world championship), they eventually may be prevented from attending events.
It’s fortunately never happened at any event I’ve worked at, but an examples of some things that would get a player disqualified would be failing a deck legality check unless the player fixes it immediately, cursing excessively, annoying other players and refusing to stop when asked, being caught cheating, wearing inappropriate clothing/not exercising good personal hygiene, or drinking alcohol or being drunk/high.