One of the defining features of Rugby League during its 100 or so year existence has been the readiness of administrators to make innovative rule changes in a continuous drive to improve the sport. Right from the outset the fledgling Northern Rugby Union was keen to establish an independent identity and by 1907 major differences between its matches and those played under Rugby Football Union rules had been established.
A central theme of the new rules was the need to encourage a more open style of play in order to attract paying spectators to help fund the sports professional clubs. So in most cases they were aimed at increasing the speed of the game and providing greater scope for attacking play. Perhaps the most distinctive change was a reduction in the number of players to 13 a side. But equally important alterations were made in order to regulate the contest for possession. After a series of experiments a play-the- ball rule was introduced to replace the rucking and mauling which often slowed down the game after each tackle, whilst line outs were abolished and the scrum became the means by which the ball was brought back into play after it had crossed the touchline.
The new rules also helped to enhance the identity of Rugby League as it took off in Australia and New Zealand and their success can be gauged by the fact that no more major alterations were made for over half a century. When the next significant change did come it was made to address the problem of teams retaining possession for long periods of a game. A number of suggestions and experimental alterations were made, including proposals for a return to the Rugby Union rule of releasing the ball after the tackle. Finally in 1967 it was decided that the number of times a team could retain possession after a play-the-ball should be limited to four tackles before possession was contested in a scrum. But although the change was successful in opening up play it was felt that 4 tackles did not provide enough time in possession for more structured attacking options to develop and an increase to six in was made 1972.
For players like Ken Senior, whose career spanned this last change, the introduction of limited tackles meant a major rethink on tactics. But they quickly adapted and the six tackle rule subsequently became a pivotal feature in the way the game is played.