Hurstwic is a Viking-age reenactment group in New England which plays a reconstructed version of knattleikr at some of their events.
Unstated, but evident, in the Hurstwic reconstruction is the notion that knattleikr is a member of the football family. As in football games, a ball is to be transported to the end of the field to score; unlike most, the players are also equipped with sticks, which are used both to start the plays and to impede the progress of opposing players. Given their placement of knattleikr in relation to other games, it's a great reconstruction - simple, but with the essence of the family in place, and with rules that make sure the ball will periodically be struck with the sticks and fly across the field.
What follows is Hurstwic's rules, excerpted from their website.
Two opposing teams face each other in lines. Each player has a bat. One ball is used. Each play begins with one team in possession of the ball. One member of that team throws the ball at the opposing team. Using their bats, the opposing team tries to hit the ball back to the first team before the ball touches the ground. If the ball is hit successfully, both teams attempt to take possession of the ball. The team that takes possession of the ball attempts to carry the ball down the field, through the opposing team, to the end of the field to score.
The ball may be passed from one player to another. The opposing team may obstruct the player with the ball by tackling, tripping, or other means, using arms, legs, bats, or whatever may be at hand. The ball remains in play even if dropped, stolen, or intercepted, so if the opposing team captures the ball, they are free to run it to their end of the field and score.
Play stops only when: a score is made; or the ball goes out of bounds; or the player possessing the ball is so thoroughly smothered by opposing players that he has no options for further play.
If when the ball is first thrown, the opposing team fails to hit the ball before it touches the ground, or if they hit it out of bounds, play stops and the ball is returned to the first team to start a new play.
If the ball is in play and goes out of bounds, possession of the ball is taken from the team that last touched the ball, and given to the other team to start a new play.
If the ball is in play, and the team possessing the ball fails to score, the ball is given to the other team to start a new play.
The team who has scored the most number of times when the game ends is declared the winner. The game ends when only one player remains standing, or when all the ale has been consumed.I'm going to be organizing a game of knattleikr according to these rules at a Viking-themed reenactment event in my own area late next month. While Hurstwic doesn't report any serious injuries, I do intend to add an instruction that the bats are not to be wielded as weapons and that players should refrain from doing anything that shows an obvious disregard for safety - the sagas definitely do report a few serious knattleikr injuries that are a part of the game's history I'd rather minimize in modern times, and there's a difference between "may obstruct" and "may attack." But in any case, Hurstwic's experience demonstrates this ancient sport can be approximated for modern players, and remains enjoyable many centuries later. Indeed, the essence of the game is not dissimilar from modern-day rugby codes, save that the players in rugby do not carry large sticks with which to check their opponents.