Razz is a game in which the structure is the same as seven-card stud. Essentially the only difference in rules between the two variants is in how hand strength is determined. In seven-card stud, the highest 5-card hand wins, while in razz, the lowest 5-card hand wins. This makes it fundamentally different to most other poker variants.
Razz also happens to be one of the poker variants frequently included in mixed games, such as HORSE or 8-game. Because it is so similar in structure and game play to stud, and usually occurs adjacent to stud in the order of games, you will frequently find people at lower limits online trying to play stud during some of the razz rounds!
As stated above, razz has the same structure and format as seven-card stud. Each player is dealt two cards face down (that only they can see) and one card face up (that everyone can see). The two face down cards are called "hole cards" and the face up card is called the "door card."
The player with the highest numerical value door card must post the bring-in (mandatory bet), or may instead put in a full sized bet (complete) before 4th street. In the case that two or more players have the same numerically highest door card, the bring-in is determined by suit, where the suits are ordered spade, heart, diamond, club (from highest to lowest).
This means the King is the worst door card since aces are low in razz. The bring-in is typically about 1/3 or 1/2 the size of the regular bet size. After a bring-in, the next player to act may call the bet or raise to a full sized bet. Once the bet has been completed, play continues with each raise being of a regular bet size amount.
Once betting is completed, a face up 4th street card is dealt out to each player still in the hand. The player with the lowest, showing hand (two cards per player are now face up) acts first, so as to give a positional disadvantage to the apparent best razz hand.
Once the betting is completed, 5th street is dealt face up, and so on. After 5th street, the bet size doubles for the remainder of the hand. 6th street is also dealt face up, but 7th street is dealt face down, and whoever last opened the betting on 6th street will be the first to act after 7th street.
The "worst" hand wins in razz, so the only hands that typically win are no pair hands with low numerical cards in them. The strongest razz hand is 5♠4♥3♥2♣A♣. Flushes and straights do not count for anything in razz, so 5♦4♦3♦2♦A♦ suited does not lose to a one pair hand like 8♦8♣5♣2♦A♠. Suits are essentially meaningless in razz except for in bring-in tie-breaker situations, so 7♥6♣4♠3♣A♣ and 7♦6♦4♥3♦A♦ would tie if they both made it to showdown.
Razz hands are made a little tricky by the fact that only 5 cards are used when 7 are available, but this is in essence the same as in hold'em. For example, 5♠3♣4♥2♥5♦A♥5♣ is a fantastic hand, because despite holding three 5's, this player's razz hand is 5♠4♥3♣2♥A♥.
In razz, the highest valued card in each final 5-card hand is used to determine which hand wins. For example, 8♣7♦6♣4♥3♦ would beat 9♦5♦4♦2♣A♣, because it's the highest card in the 5-card hand that is counted first.
Similarly, if there is a tie for lowest top card, the next highest one is used – so 9♦8♠5♣4♠2♥ loses to 9♠7♣6♦5♠4♥. Here are a couple more examples, with the full 7-card hands included:
In razz, your most important strategic move is to be picky in your starting hand selection. 32A is of course the strongest starting hand, and any starting hand with only cards in the wheel (ace through five) is very strong. But just as important is to look at what other players are holding.
On the "flop," you can see one card from the hand of each other player. If they are showing higher cards that we aren't interested in, or the same cards that we already have, that's good. If they are showing cards that we know we want to draw to, that's bad. But seeing cards that match our own is especially important because it means it is much less likely for us to get paired cards in our hand.
Another important part of razz strategy is utilizing your door card. If you have lowest showing door card and the action is folded to you, it is typically correct to raise, even if your hole cards are significantly weaker and taint your absolute hand strength. You can steal blinds and antes, as players with higher door cards will often fold, and if they don't, you can usually infer that their hole cards are particularly good.
Razz is perhaps the most popular "lowball" poker variant, but it is still not on top of the poker world by any means. As with most of the lesser-played variants of poker, razz will often feature a lot of weak players, so with some hand-reading, good starting hand selection, and a bit of experience, you start crushing the game!