Chariot racing used to be very, very popular in the Roman and Byzantine empires. Here's a couple anecdotes:

• The highest-paid athlete in all of history was likely the charioteer Gaius Appuleius Diocles (2nd century AD). He earned enough in his lifetime (about 15 billion in today's dollars) that he could have fed all of Rome for a year.

• During the reign of the Byzantine emperor Justinian (482-565), the supporters of the chariot teams, the Blues and the Greens, were so numerous that they were able to threaten the stability of the empire during the Nika Riots. Justinian allegedly nearly fled the empire in fear of the rioting fans, but his wife convinced him to stay and orchestrate a massacre of the partisans instead. 30,000 rioters (about 10% of Constantinople's population) were killed while gathered inside the Hippodrome, the capital's chariot-racing arena.

The other ancient Olympic sport that no one competes in anymore but was huge in the ancient Greek world starting in 776 B.C. was the hoplitodromos. An event that is a 400 yard sprint with 59 pounds of armor with its best athlete being Leonidas of Rhodes who won it for 4 straight Olympics in 164 BC, 160 BC, 156 BC and 152 BC games. So there is a fun fact for this incredibly informative post.

ullamaliztli http://www.aztec-history.com/aztec-ball-game.html

It was a ball game that was extremely popular throughout Mezo America until the destruction of the Aztec civilization by the Spanish.

It was played on a large court with two teams. There was a single hard rubber ball, and the point of the game was for a team to get the ball through a high vertical stone hoop place on one of the walls surrounding the court. The players could only use their elbows, knees, hips and head, and the ball could not touch the ground.

Some of the games finer details are fuzzy because there has never been a complete "rule book" for it so to speak, found.

Buddy I have something for you.

Ever hear of Fox tossing?. It is an old blood sport once popular among European aristocracy in the 17th and 18th centuries. Read this and also pay attention to what it says about the famous tossing contest held in Dresden by Augustus the Strong, Elector of Saxony.

It is quite fascinating actually. It is safe to say this is a dead sport.

Pankration doesn't exist any more in its traditional form, for fairly obvious reasons.

For those who don't know what Pankration is, it was a combat sport with no weight divisions or time limits (ie, the fight would continue indefinetly). The only two rules strictly enforced were a ban on biting and eye gouging. The contest itself usually continued uninterrupted until one of the combatants submitted, which was often signalled by the submitting contestant raising his index finger. The judges appear, however, to have had the right to stop a contest under certain conditions and award the victory to one of the two athletes; they could also declare the contest a tie. In pankration competitions, referees were armed with stout rods or switches to enforce the rules.

Athletes would typically fight four fights over the course of several days, each fight being an elimination fight.

Chunkey was a huge game for awhile among native groups north of the Rio Grande. The Mississippian and southeastern peoples were huge players of this game until its popularity declined in favor of other activities such as lacrosse, although it was still being played among some groups during colonial times. Chunkey consisted of a circular stone, sometimes with concave sides, which was rolled on a large, flat area of beaten earth with two teams each having long narrow sticks to use.

George Catlin recorded how the game was played in 1832,

The game of Tchung-kee [is] a beautiful athletic exercise, which the Mandan seem to be almost unceasingly practicing whilst the weather is fair, and they have nothing else of moment to demand their attention. This game is decidedly their favourite amusement, and is played near to the village on a pavement of clay, which has been used for that purpose until it has become as smooth and hard as a floor . . . The play commences with two (one from each party), who start off upon a trot, abreast of each other, and one of them rolls in advance of them, on the pavement, a little ring of two or three inches in diameter, cut out of a stone; and each one follows it up with his ‘tchung-kee’ (a stick of six feet in length, with little bits of leather projecting from its sides of an inch or more in length), which he throws before him as he runs, sliding it along upon the ground after the ring, endeavouring to place it in such a position when it stops, that the ring may fall upon it, and receive one of the little projections of leather through it.

Men used to compete in Cornish wrestling as late as the late 19th century in Cornwall, England, and all over the world wherever there was a significant Cornish population--usually miners. It was a style of wrestling where the competitors wore tough jackets and threw each other while grabbing his opponent's jacket. Admittedly there are still some few Cornish wrestlers around, but it's a sport that's certainly not as well known or popular as it once was.

I'm sure there are countless variants of wrestling with their particular rules and techniques from many cultures that have largely faded away in modern times.

Arguably western fencing.

Fencing as taught in the renaissance era were radically different from today's Olympic fencing. If you put a modern fencer and a renaissance era fencer in the same room, they wouldn't even recognize what the other was doing.

Tug of war is still popular, but not as an olympic sport. I'd figure that the version played by the vikings using animal skin and a fire pit, has few adherents today.

The mexican government is trying to revive a number of ancient sports including pelota purepecha, pelota mixteca and the like. Pelota purepacha, best described as field hockey with a flaming ball, is the most popular today with ~800 players.

Unfortunately, I'd have to regretfully state that competitive olympic poetry, fisherman's joust, naumachia etc are more akin to entertainments/games and should not meet your definition of sports, and some may even be played in a limited form.

Chariot racing and the meso-american ball game (my first choices) have already been mentioned; Fox running, bear baiting, cock fighting and other animal 'sports' etc have also been mentioned, I think. Some are still followed today but relatively suppressed/frowned upon in many areas.

Ollamaliztli was a mesoamercan ball game played in various iterations by at least the Maya and Aztec civilizations. Like most everything else surrounding those civilizations, it stopped being played after European conquest of the region.

Cricket essentially died in the United States, despite being the most popular sport until the Civil War. The first ever international cricket match was actually contested between the US and Canada.

It's popularity rapidly declined with the rise of baseball in the years after the Civil War.

Source: http://www.espncricinfo.com/magazine/content/story/141170.html

A more recent example of a sport that used to be popular (at least in Europe) and now is dead is field handball. It was played even at the 1936 Olympic Games. A game of field hanball looked like this. Only the indoor variant is alive today and is called just handball in Europe or team handball or European handball in the USA.

[Goose Pulling] (http://en.wikipedia.org/wiki/Goose_pulling) or "Greased goose Grabbing" was popular in the seventeenth to nineteenth centuries. It exists in other variants today, and is still being practised in Belgium on holidays.

Soule/Choule was a kind of ancestor of rugby, played with an inflated animal bladder on a HUGE field. It was traditionally played between two parishes and the goal was to bring the ball (sometimes with sticks, sometimes just holding it) in front of the opposite parish's church, with no time limit - some games are said to have lasted several days. Team sizes varied from 20 to 200 players.

It originated in Northern France (Normandy/Picardy) and was really popular for most of the Middle Age onwards - the first textual evidence of it being played is a 1147 charter, and the last recorded games seem to have taken place around 1930. Some people are apparently trying to revive it these days, but it's definitely extinct as a form of popular entertainment, probably replaced by soccer (definitely the most popular French team sport these days).

From contemporary texts, it seems to have been a pretty rough sports, with injuries such as broken bones not uncommon. It's related to other early ball games such as Caid (Irish) and Knattleikr (Viking).

Trugo, a sport revolving around hitting a rubber wheel with a mallet swung between your legs, popular in Melbourne, Australia in the early 20th century, is heading this way.

Would not archery be a sport that has disappeared from the masses? It was performed at fairs and at courts through out the middle ages but now it only exists as an elite sport for the Olympics really.

Gaelic Football and Hurling were in danger of becoming extinct before, as part of the Gaelic revival, the GAA (Gaelic Athletic Association) was formed to champion them in Ireland.

London Skittles was a version of skittles - similar to ten pin bowling. At one time played in pubs all across London, it has dwindled to the point where its only played in one club in London.

Nine pins are placed on a wooden frame at the end of an alley and a 'cheese' (a large and heavy ellipsoid made from lignum vitae) is thrown through the air to collide with them. If the pins are all knocked down, then it's declared a 'floorer' and play moves to the other participant. If pins remain, the initial thrower continues to try to eliminate them, similar to the familiar ten pin bowling.

The game was once sufficiently popular to allow for 'stickers' - people who picked up the pins to reset the frame - to make a living doing so. Charles Dickens and AP Herbert were regular players. Since World War II, the game has almost completely disappeared and few have now heard of it.

Website of the last remaining London Skittles club: http://www.londonskittles.co.uk/