The need for an "offside" law goes back to the early years of the game. A player was "off his side" if he was standing in front of the ball, that is, between the ball and the opponent's goal. To the Sheffield Association, this didn't matter at all! There was no offside rule, and players known as "kick throughs" were positioned permanently near the opponents goal.
The people who drew up other "rules of the game" in the mid nineteenth century had been brought up with the idea of keeping all players "behind" the ball, disallowing the forward pass, and making progress towards the opposition's goal by means of dribbling with the ball or in a scrum. For a game of soccer to flow freely, it was essential to allow the forward pass, thus raising the need for an offside law. The Cambridge rules of 1848 stated that it needed three of the opponents side between a forward player and the goal for him to be "onside". However, the Uppingham rules of 1862 remained strictly against the forward pass; "if the ball is kicked by his own side past a player, he may not touch it, or advance, until one of the other side has first kicked it, or one of his own side, having followed it up, has been able, when in front of him, to kick it". The first set of Football Association rules agreed with the Uppingham idea.
As football developed in the 1860s and 1870s, the offside law proved the biggest argument between the clubs. Sheffield got rid of the "kick throughs" by amending their laws so that one member of the defending side was required between a forward player and the opponents goal; the Football Association adopted the Cambridge idea of three! Finally, Sheffield came into line with the F.A., and "three players" were the rule until 1925.
The change to "two players" rule lead to an immediate increase in goal scoring. 4,700 goals were scored in 1848 Football League games in 1924/25. It rose to 6,373 goals (from the same number of games) in 1925/26.