 As someone who just started to get into soccer a few years ago, the most confusing rule is probably offsides. This is because while offsides is a thing in a few American sports, it's always based on a line that doesn't move, only the players do. So in American football, you can't cross the line of scrimmage, which is where the ball is sitting and not moving. In hockey, it's all about the blue line, which is literally drawn onto the ice. But in soccer, the line that you need to stay behind to stay onside is moving all the time, because it's determined by a player, and which player it is, is always changing. Also, you have to kind of be looking in two places at once, which is a bit difficult if you are not a chameleon. So it's a little tricky to get used to, but once it clicks for you, you can pick it out quite easily. As with any offsides rule, we're trying to stop players from just standing next to the goal and waiting for our teammates to pass it down to them. So in its most basic terms, the rule says that there have to be two defenders between the offense's leading attacker who's involved in the play and the goal when someone kicks the ball to him. And yes, the goalie in this case does count as a defender. So the most common way you're going to see a player go offsides is if the ball is back here and the attacker moves to run toward the goal and receives the ball about here. This attacker is offsides because between him and the goal, there is only one defender. In this case, it's the goalie. Now the easier way to visualize this is actually to look at the defenders first. So with this player here being the second to last defender, we can draw a line parallel to the goal line through him. And if any part of our attacker's head or body or legs is over this line, then he is offsides. If you play either of the soccer video games, Pes or FIFA, they'll both show replays with a line just like this every time someone goes offsides. And so will some replays on TV broadcasts. So you might be asking, at what point do we draw this line then? Is it always there? It is not. It is drawn at the moment that the ball is kicked, not when the leading attacker actually gets the ball. So ideally, this attacker will start to sprint and then right when he is level with the second to last defender, his teammate will pass him the ball. This will put him way behind the defender by the time he actually gets the ball. On the other hand, if his teammate passes the ball a second too late, then he's going to be offsides, so it's all about timing here. In order to be called offsides, a player must be active in the play, meaning that if the ball is over here and our attacker is running around up here, he is in an offside position, but nobody's going to blow the whistle and call them offsides until someone kicks in the ball or he becomes involved in the play somehow. So if our player here goes offsides, then what happens? You may have noticed that during soccer games, there are referees with flags running up and down the sidelines. One of the toughest parts of their jobs is to make sure that players do not go offsides, and typically they will run as to remain parallel with the leading attacker, and when he goes offsides, then they'll raise their flag to signal that he is offsides. When this happens, the whistle will blow and then the other team gets the ball, a free kick from wherever that attacker went offsides. It's not so bad when it's just one sprinting player, but the situation can get fairly complicated when a team is attacking and lots of their players are around the box because defenders, and therefore the offside line, is always moving back and forth. There's a lot of moving parts to keep track of, and this has actually resulted in a defensive strategy called the offside trap in which defenders will wait level with an attacker until the last second at which point they will run forward, thus putting the attacker offsides. Of course, there is some risk here because if you are a step too slow and the attacker manages to stay onside while you are running away from your own goal, well then good luck trying to catch up to him. Sometimes the offside trap is employed on free kick situations, which can result in offsides. However, during throw-ins, corner kicks, and goal kicks, attacking players cannot be offsides, and so they can stand wherever they want when receiving the ball. So to recap, the offsides line is determined by the second to last defender in front of the goal at the moment that the ball is kicked to the leading attacker who is involved in that play. Sometimes defenses will do this on purpose, which is called the offside trap. You can be offsides during a free kick, but not a throw-in, corner, or goal kick, and going offsides will result in a free kick for the other team. So once you get used to it, like I said, it's not really that difficult to understand. The hard part is just being able to pick up on it at full speed.