KIRKWALL, Scotland — William Thomson’s family had played this sport for centuries, so he understood that he needed to choose between two strategies for the annual Christmas day ba’ game.

The scrawny 17-year-old could fight for the ball in the center of the riotous scrum, where more than 300 men would function as a human juicer, turning his face red, then purple. He would be scratched, punched, kneed, and bitten. His ribs might break. He could pass out unconscious.

Or, Mr. Thomson could follow convention for players his size and stay near the edge of the scrum, pushing the pile. This would work well unless the ball popped out and the mob changed direction. Cars, gravestones, houses, strollers, hotel lobbies — all had been kicked, shoved, or trampled in pursuit of the ball during previous games. Anticipating such a stampede, business and homeowners in town had nailed wooden planks across their doors and windows. “If you’re on the edge of the scrum and it turns on you,” one veteran player said, “then you might as well be dead.”

This, Mr. Thomson decided, was his safest option.

He never considered not participating. The men in the Thomson family — like the men in most families here — have played this game since at least the mid-1600s. It is one of the oldest and most physical sports, and it’s almost certainly the most simple. Half of the men in Kirkwall, called Doonies, try to push a small ball into the sea using any means necessary. The other half, called Uppies, work to push the ball to a wall one mile across town. The ba’, which refers to both the game and the ball with which it is played, can last anywhere from four minutes to nine hours in freezing temperatures and hurricane-force winds.

The ba’ is played nowhere else. It has persisted in Kirkwall because its basic tenets are congruent with life on these Orkney Islands in northern Scotland. If you’re tough enough to survive in this old Viking territory, in a frostbitten town of around 6,000 bordered by white-capped seas, then you don’t worry about relaxing on Christmas and New Year’s Day. You put on steel-toe boots and a rugby shirt and walk downtown to the almost 900-year-old St. Magnus Cathedral, ready for hell.

The Uppies and Doonies squeezed into a tight pack last Tuesday afternoon in front of the cathedral, where they waited for a former player, standing in front of a cross, to throw the ba’ into the middle of the scrum. Mr. Thomson, a Doonie, stood on the edge as planned. He had wrapped duct tape around the bottom of his frayed jeans to ensure that nobody could rip them off. He had hastily patched two holes in the back of his rugby shirt, mending relics from one of last year’s games.

The ba’ flew over Mr. Thomson’s head and disappeared into the chaos behind him. A few Uppies circled behind Mr. Thomson for a better angle to push the scrum into a side alley. Doonies circled behind those Uppies and tried to pull them away. Before Thomson realized what had happened, he was in the center of the pack, his arms trapped at his side.

For almost 30 minutes, the scrum deadlocked in the 15-foot-wide alley. Two hundred Uppies grunted and pushed in one direction; 115 Doonies held their ground. Thick steam rose from the pack, and Mr. Thomson couldn’t find fresh air. He called out for space, but the screaming mob drowned his request. His eyes rolled backward, and his head fell on his shoulder. A nearby Doonie slapped him across the cheek and poured water on his face, desperate to wake him. Thirty seconds passed before two spectators climbed down from the alley wall and stepped on the heads and shoulders of ba’ players to reach Mr. Thomson. They pulled his limp body from the pile and carried him 100 yards away.

Once he awoke, Mr. Thomson asked his girlfriend what had happened. His ribs ached, but he felt otherwise okay. A few friends stopped by to check on him, and one offered a flask of whiskey.

“Thanks,” Mr. Thomson said. “I need this to get my nerves back.” He took a swig and handed back the flask. Then he lifted himself up over a wall and dropped back into the riot.

Three days before the Christmas ba’, Ian Smith diagrammed game strategies while sitting next to a coal fire in his house overlooking the town. At 60, Mr. Smith is one of the oldest men still participating in the ba’. He has played for 45 years, never missing the twice-annual game despite heart surgery, a hip replacement, nine broken ribs, and two knee surgeries. A butcher and a lifelong Orcadian — he refuses to call himself Scottish — Smith identifies first and foremost as a Doonie.

When the ba’ game was first played in Kirkwall, teams were divided by whether a player was born closer to the ocean (a Doonie) or the wall (an Uppie). A hospital opened in Kirkwall about 50 years ago and became the location for all births, so now family history determines the teams. Newcomers to the island usually move into recent housing developments near the wall and declare themselves Uppies, which has created an imbalance. With almost twice as many men, the Uppies have won 15 of the last 16 ba’s.