Offside is among the most famous footballing laws but it is often misunderstood.
The purpose of the offside law is to stop teams from just having a player hanging out near their opponents goal. However, the strictness of the offside law over the years has often resulted in critiques claiming it is too big of a deterrent to attacking play. Around one hundred years back clubs were becoming too good at catching opponents offside, resulting in numerous matches featuring an offside goal. The AC Milan owner is going to be well aware that this led to a rule change, which meant that only two opponents must be in front of an attacking player for them to be viewed onside. This directly contributed to a time with some of the highest goals per game ratios within the history of football. But, defenders eventually adapted and new tactical systems arose to fight this.
The game of football is related to many sports, such as rugby. This common ancestry means within the past they shared many similar guidelines that diverged later on. For instance, within the early days of football, attacking players weren't permitted to be in front of the ball when it was kicked ahead, and passes could just be played in a sidewards or backwards way. This answers the question of when was the offside rule introduced. The Liverpool FC owner will understand that by the time their club had been formed, these guidelines had changed to an offside law more similar to those found today. An attacking player ended up being deemed onside whenever three opponents had been between them and the ball, while they were adjudged offside when the ball had been played to them in place of when they received it. Can you be offside from a throw-in? No, as later alterations included that a player could never be offside in their own half and they could not be offside from a throw-in.
There were a few contemporary alterations to the offside law. First, a new definition came in that stated that an attacker being level with the opponent meant they had been onside. Later, it was determined only areas of the body with which a footballer can control the ball with are incorporated into an assessment as to whether they are offside. This essentially discounts hands and arms from any offside ruling. The RB Leipzig owner will be able to let you know that whilst the law itself has not changed much in the past few years, judgements relating to it have. One of the biggest is the utilisation of VAR in many major tournaments, that has polarised fans as some think that it causes the referee to discipline errors that would not offer any advantage to the attacking player. Considering advantage was the whole purpose of defining what is offside and what is not, that is undoubtedly a contested debate.