Dirty Schultz is a Seven Card Stud variant similar to Follow the Queen and also goes by the name Follow the Pair.
It plays exactly like Seven Card Stud, starting with three hole cards, one face down, and the player with the highest card showing starts the betting. The next three rounds will see each player dealt a face up card, with the betting starting with the player who has the best card showing. Finally the fifth round will see each player dealt a seventh hole card dealt face down.
The only difference in Dirty Schultz is if a player has a natural pair showing (So for example they have two Jacks face up, a pair made including the face down card does not count) the next card they are dealt becomes a wild card. So for example if you need a 6 to make three-of-a-kind, the next card out would count as a 6 no matter what its actual value.
If a second natural pair is dealt, the new wild card replaces the old wild card, meaning that the original wild card reverts back to its original value.
If the final face up card completes the natural pair, nothing is wild. An alternate variant of the game states that the wild card is instead dealt as a community card, and all cards of the same rank are wild for all players. So for example if a player is dealt a natural pair of Queens and the next card is dealt to the community which is an Ace, any Ace held by any player is now wild.
A less popular variant of the game states that if a player has any pair including using their face down card then the next card is wild. There are variations as to when the player must announce they have a pair, but it is usually when it is their normal turn to act.