So, what's the offside rule?

Time for some copypaste from wikipedia!

Offside is one of the rules of association football, codified in Law 11 of the Laws of the Game. The law states that players in an offside position, when the ball is touched or played by a teammate, may not become actively involved in the play. A player is in an offside position when he or she is in the opponents' half of the pitch and closer to the opponents' goal line than both the ball and the second-to-last opponent (usually the last defensive player in front of the goalkeeper). Being in an offside position is not an offence in itself; at the moment the ball touches or is played by the player's team, the player must also be "actively involved in the play" in the opinion of the referee, in order for an offence to occur. When the offside offence occurs, the referee stops play and awards an indirect free kick to the defending team from the position of the offending player.

The offside offence is neither a foul nor a misconduct, players are never booked or sent off for offside. Like fouls however, any play (such as the scoring of a goal) that occurs after an offence occurs but before the referee is able to stop play is nullified.

One of the main duties of the assistant referees is to assist the referee in adjudicating offside their position on the sidelines giving a more useful view sideways across the pitch.
Assistant referees communicate that an offside offence has occurred by raising a signal flag.

Now let's be a little more specific

Commiting an Offside Offence

A player in an offside position is only penalised if, at the moment the ball touches or is played by one of his team, he is, in the opinion of the referee, involved in active play by:

• interfering with play
  
• interfering with an opponent
  
• gaining an advantage by being in that position

No Offence

There is no offside offence if a player receives the ball directly from:

• a goal kick
  
• a throw-in
  
• a corner kick

Well, you know the basics and the list of rules that you need to know to stop being in ♥♥♥♥♥♥♥ offside.

But just for avoiding some dumb offside lets put some examples on.

Example 1


This is offside because the red number 10 is in front of all of the defenders, leaving only the goalkeeper back which isn't enough players to play him onside. This position may have been forced by the defenders moving forward in what is called the offside trap.










Example 2


Here we can see that the blue number 3 defender has fail to move up the field with rest of his defence and played the red number 9 onside. This is a classic example of where the offside trap fails












Example 3


The offside rule exists to stop goal hanging, where a player stands next to the opposing teams goal keeper in the hope that someone can get the ball to him (probably using a long ball), so he can get it past the goal keeper. Which would make for a very boring game.

Hard to master, but once you do, it's vital in a good defense tactic.

Concept

Pioneered in the early 20th century by Arsenal FC and later adopted by influential Argentine coach Osvaldo Zubeldía, the offside trap is a defensive tactic designed to force the attacking team into an offside position. Moments before an attacking player is played a through ball, the last defender(s) move up field, isolating the attacker into an offside position. The execution requires careful timing by the defence and is considered a risk, since running up field against the direction of attack may leave the goal exposed.

Examples


Here, we can see than all the Siena defenders leave the area as soon as Balotelli makes the cross. Awesome defensive play.









Again, a good freekick outplayed by a better offside trap. This time from the great Barcelona.










But sometimes, it fails. And when it does you better start running to the middle cause it's a certain goal. This is an example made by my compatriot Lionel Messi how didn't interfere in the play to let Pedro reach the ball and pass it back to him. Outstanding mental play.









Last one and I stop, I promise. This is in the Liga MX (or Mexican League) between Chiapas and Morelia. Here we see that Chiapas defender leave to late the box, puts onside all the attackers and give them a very easy goal. That's shameful.

So, yeah. Now that you've read it all, please stop putting yourself in offside all the time or putting the attackers in onside all the time.

Please, a centimeter makes the difference between a good defense and a goal.

Any question, leave it in the comments. Oh, and sorry for the bad english.