Friendly robber
The robber may not be placed on a hex adjacent to a player who has 2 or fewer victory points. If every hex touches such a player, the robber goes to the desert instead. Keeps an early setback from snowballing into an unwinnable game.
What to know before you play it
This one is not a house rule at all — it is an official Catan variant. Klaus Teuber published it in Catan: Traders & Barbarians (2008), where it sits alongside the Fishermen, the Rivers and the Barbarian Attack as a small rule that may be combined with any scenario. Most tables that play it have no idea it is in a box.
The threshold is the part worth agreeing out loud before you start. The published wording protects a player with two victory points or fewer — so a player on 3 is fair game, and everyone starts the game protected, because everyone starts on 2. Tables that say "let's play friendly" without naming a number end up arguing about it mid-game, and online implementations differ from each other, which is where most of the friction comes from.
Three edge cases the short version leaves out. If no hex is legal, the robber returns to or stays on the desert. If a protected player has a settlement on the desert, you still take nothing from them. And the discard rule is untouched: a 7 still costs anyone holding more than seven resources half their hand, protected or not. The official FAQ also settles the obvious question — victory points on face-down cards do not count when you work out who is protected.
What it costs. Robbing the leader is usually the correct play, and this rule takes some of that away, so it is doing something to the game rather than just being nice. It also quietly favours whoever opened on wood and brick, since they are the ones everyone would otherwise rob while the roads go down. It is aimed at family tables and mixed-experience groups; a table that plays to win will feel the difference.
Does your table play this?