Brockian Ultra-Cricket, described as "a curious game which involved suddenly hitting people for no readily apparent reason and then running away", is a fictional sport.

It first appeared in the original BBC radio series The Hitchhikers Guide to the Galaxy, and later in the novel Life, the Universe and Everything, written by Douglas Adams. In the books, the sport is first named in the first novel; the name comes from Jonny Brock, a friend of Adams.

Its rules (as told from the book) are as follows:

Rule One: Grow at least three extra legs. You won't need them, but it keeps the crowds amused.
Rule Two: Find one good Brockian Ultra-Cricket player and clone him off a few times. This saves an enormous amount of tedious selection and training.
Rule Three: Put your team and the opposing team in a large field and build a high wall round them.
The reason for this is that, though the game is a major spectator sport, the frustration experienced by the audience at not actually being able to see what's going on leads them to imagine that it's a lot more exciting than it actually is. A crowd that has just watched a rather humdrum game experiences far less life-affirmation than a crowd that believes it has just missed the most dramatic event in sporting history.
Rule Four: Throw lots of assorted items of sporting equipment over the walls for the players. Anything will do — cricket bats, basecube bats, tennis guns, skis, anything you can get a good swing with.
Rule Five: The players should now lay about themselves for all they are worth with whatever they find to hand. Whenever a player scores a 'hit' on another player, he should immediately run away and apologize from a safe distance.
Apologies should be concise, sincere and, for maximum clarity and points, delivered through a megaphone.
Rule Six: The winning team shall be the first team that wins.

It is said that the rules of Brockian Ultra-Cricket are so controversial that the civilizations which play it spend more time in a state of war over their interpretation than they do actually playing the game; it is mentioned that the rules are so lengthy and complex that the one time they were collected in one place for reference, a black hole was formed out of their mass. It is believed that "in the long run, a good solid war is less psychologically damaging than a protracted game of Brockian Ultra-Cricket", so this may be a good thing.

All of these rules and periphery information given by Douglas Adams are parodies of the real cricket: cricket matches can be notoriously protracted, there are frequent debates over the interpretation of the rules (eg, Ricky Ponting's attack in 2005 on England's use of substitute fielders), possibly due to certain rules' complexity.

Brockian Ultra-Cricket was the inspiration behind the naming of Tim Astley's play-by-e-mail simulation, Ultra Cricket (external site). The similarities end with the name, as Ultra Cricket simulates regulation Test and one-day matches.