Table Stakes
The rule that you can only bet the chips you had on the table when the hand began.
Table stakes is so fundamental to modern poker that players forget it's a rule at all: no reaching into your pocket mid-hand, no betting the watch, no "I'll owe you" against a bet. Whatever is in front of you at the first card is your maximum exposure. It's the rule that killed the movie scene where the hero raises the ranch.
Its main practical consequence is the all-in and the side pot. You have $60 left; an opponent with $400 bets $100 on the turn. You can call your $60 — you can't be forced to fold for lack of funds — and the $40 excess, plus any further betting, goes into a side pot you can't win. If three players are in with three different stack sizes, the dealer builds a main pot and side pots in order, and each short stack contests only the pots they paid into. Anyone dealing a home game should be able to do this in their sleep.
Table stakes is a fairness rule, and home games should enforce it strictly: it stops the richest player at the table from buying an edge by simply threatening more money than anyone else has. It also means buy-ins, rebuys and top-ups happen between hands, never during one — and the house should state minimum and maximum buy-ins up front, because those numbers are what make the stakes honest.
One corollary worth knowing: chips behind your stack aren't in play, so a mountain of winnings in front of you doesn't protect you from a bad night — every hand resets your risk to what's on the felt. Track results by buy-ins in and chips out, and the table stakes rule takes care of the rest.