The sport's first set of written rules date back to 1845 but have been open to revision ever since. Those rules had to be re-defined in 1863, as rugby and football began to follow diverging paths.

The rules were still open to local interpretation in 1871, when Scotland and England undertook the first official international match, with both sides that day having different ideas of how the game was to be officiated.

Today rugby union's rules are the responsibility of the International Rugby Board (IRB) and their regular redrafting in recent years has been a major source of controversy.

Improving the game as a spectacle and making it safer as players increase in size, fitness and power have been major contributing factors to these changes. Sometimes both issues have been involved. When lifting was introduced in line-outs, for instance, to try and make them less chaotic, it also had to be stipulated that players should no longer be tackled in the air to avoid serious injuries.

Many rule changes have involved the breakdown, with administrators on the one hand wanting to allow both sides to contest possession, but on the other hand also trying to keep the game flowing rather than allowing the ball to disappear under a pile of bodies.

Traditionalists, however, argue that rugby union is in danger of being diluted into another form of rugby league or sevens if traditional forward tactics - like rolling mauls - are declared illegal.

Others, however, argue that safety should be paramount, even leading to calls that scrums, traditionally one of rugby union's great trials of strength, should be defused or even banned.

Arguably the greatest law change came in the late 1960s. Until then, no substitutes of any kind were allowed. Today, a bleeding player must be replaced, at least temporarily.