Usually, one transgression by itself wouldn't be enough to bring such a punishment to an otherwise clean account, but the IFS works on an escalating punishment system. Breaking a minor rule, like engaging the team in useless arguments, has a minor punishment: a chat restriction. Breaking that same rule over and over again, however, doesn't prompt an endless series of chat restrictions. The severity of the punishment ramps up over time, because the goal is to eliminate the punished player's willingness to break the game's rules. If two chat restrictions don't stop the useless arguments, the system will increase the punishment to a 14-day suspension and deliver a very clear message that the continued rule-breaking is becoming a serious issue and any further instances will result in a permaban. Again, the point is to put a stop to this misbehavior. If a player is more interested in repeatedly breaking the rules than in maintaining access to their account, they'll lose access to their account.
Of course, it's possible to break major rules, like cheating, threatening people, or using chat for hate speech, and skip punishment tiers so that a clean account ends up with a 14-day suspension or even a permaban.
From Riot's support knowledgebase:
PUNISHMENTS GENERALLY FOLLOW A BASIC ESCALATION PATH:
- First Offense: 10 Game Chat Restriction
- Second Offense: 25 Game Chat Restriction
- Third Offense: Two Week Suspension
- Fourth Offense: Permanent Suspension
However, it is possible to skip to a Two Week or Permanent suspension based on the severity of the behavior in the game. Excessive negative behavior can result in a Two-Week or Permanent suspension at any time without having a chat restriction on the account.