For millions of soccer fans around the globe, the 31 days between World Cup opener and World Cup final represent the greatest month of every four years. For millions of other sports fans, however, it’s the only month every four years when soccer exists.

And while we here at FC Yahoo would love if you stuck around for the three-year, 11-month interims, we understand. We welcome all comers to soccer fandom. And we cherish your interest – so much so that we’re here to help you, the casual soccer fan, understand the beautiful game.

That’s why we’ve put together a fun little three-part series, entitled Soccer for Dummies. The goal is to foster both understanding and enjoyment of the sport. Part 1 clued you in on soccer’s terminology and linguistic quirks. Part 3 breaks down tactics, and the diverse styles of play you’ll see in Russia this summer.

[Yahoo Sports’ 2018 World Cup preview hub]

But today’s subject is the laws of the game. Soccer is actually a quite simple sport. But there are a few vexing rules that even the most seasoned fans can’t grasp. So we’ll delve into both the rudimentary and the complex.

The basics

The really basics: Soccer is contested 11-on-11. Two teams try to score goals on the opponent’s net. Matches last 90 minutes, split into two 45-minute halves. Each team has 10 outfield players who may not play the ball with any part of their arms or hands, and one goalkeeper who may. Most goals over 90 minutes wins. And in case of a tie? Usually the game will end that way. Usually.

The clock: Unlike most American sports, it’s a running clock, and it counts up toward 90, rather than down from 90. At the end of each half, the referee will add on stoppage time, a rough estimate to account for delays.

So … uh … what are the rules? In a weird way, many foul calls are subjective. The rulebook says the ref should blow his whistle for a foul when a player “charges, jumps at, kicks, attempts to kick, pushes, strikes, attempts to strike, head-butts, tackles, challenges, trips or attempts to trip” an opponent” in a manner considered by the referee to be careless, reckless or using excessive force.”

There are further definitions for “careless” and “reckless” as well. And then there are specific mentions of biting and spitting, among other things. But you really just have to watch and learn what the threshold is.

And what’s the punishment? In the event of most fouls, the opposing team gets a free kick – an opportunity to pass or shoot a still ball under no pressure. More serious fouls draw yellow and red cards (more on them later). And if the foul occurs in a penalty box at either end of the field, it results in a penalty kick: a free shot from 12 yards out, middle of the goal, only the keeper to beat. Roughly three-quarters of penalties are converted.

Advantage: Not all fouls automatically bring stoppages in play. If a ref spots an infringement by the defensive team, but realizes the attacking team still maintains an advantage despite the foul, the ref will stretch out his or her arms to signal “play on.” And, well, play will go on.

Boundaries: Like in baseball, field sizes can vary. All you need to know is that if the ball crosses over the sideline – whether in the air or on the ground – the team who did not touch it last restarts play with an overhead, two-handed throw-in. If it crosses the endline off the attacking team, the defending team’s goalkeeper puts it back into play with a goal kick – a free kick from his own goalmouth. If it crosses the endline off the defending team, it’s a corner kick – literally a free kick from the corner of the field.

And the other lines on the field? All curved lines are more or less irrelevant. The midfield stripe only matters for offside (explained later). The small rectangular box at either end of the field is purely for goal kicks. The bigger one is the most important: Inside it, a goalkeeper can use his or her hands. And inside it, a foul committed by the defending team results in a penalty kick.

Substitutions: They’re very limited. Each team only has three at its disposal (plus, at the World Cup, a fourth if the game goes to extra time). And players may not re-enter after being subbed off.

The offside rule

Ready to get confused? Let’s get confused. Because the offside rule is vexing.

It’s essentially designed to prevent cherry-picking. But unlike American football or hockey, where the offside line is stationary, in soccer it is always moving. Because the line is essentially the last defender.

So here’s the rule: When an attacking player passes the ball to a teammate – that is, at the time the ball leaves the attacking player’s foot – the teammate must satisfy at least one of three conditions:

• Level with or behind the ball; OR

• On his or her team’s own half of the field; OR

• With two defensive players, goalkeeper included, between him or her and the end line.

Alternatively, here’s how the rulebook explains it:

Those same rules apply to a saved shot and rebound. If the player who pounces on the rebound is in an offside position when the initial shot is taken, he or she is offside.

But here’s where things get weird. If a player is in an offside position and steals an opponent’s back-pass to the keeper, that is NOT offside. If the player latches on to a deflected pass? That’s a gray area.

And what if a teammate tries to play a pass to an offside player, but the ball never reaches that player? Or what if an offside player screens the goalkeeper while a teammate shoots the ball past that keeper, but the offside player never touches the ball?

That’s where subjectivity comes into play. The rulebook reads …

Actually, nah. The rulebook definition is way too convoluted. It lays out the specifics, but not before it melts your brain. You can have a look here if you want. And FIFA has some diagrams here.

Some additional notes, though:

• For offside purposes, arms are considered invisible. So if a striker is level with the last defender, but has his arm outstretched to point to where he wants a pass, he is still onside.

• A player cannot be offside on a corner, throw-in or goal kick, but can be offside on any other free kick.

• Where a player receives the ball is irrelevant – meaning a player can be offside even if the pass goes backward.

The handball rule

Ball + hand = foul … right? Kind of. Sometimes. Not necessarily.

That’s more or less how the rule is applied outside the two penalty boxes. But rules state that for a handball to be illegal, it must be “a deliberate act.” But – yes, there are a lot of buts here – the rulebook doesn’t specifically define “deliberate.”

You’d assume it means “intentional.” But plenty of unintentional handballs are called. In the middle of the field, almost any ball-to-arm contact gets whistled. In the penalty box, the question of deliberateness is often interpreted as, “Could the offending player have reasonably done anything to prevent the ball-to-arm contact?”

The word unnatural is never mentioned in the rulebook, but you’ll hear commentators talk about whether the player’s arm was in an “unnatural position” when the ball struck it. If it was, the referees often give the penalty, because they conclude the player could have done something different; if it was in a natural position, they’ll allow play to continue.

So the moral of the story is that if you’re unsure about a handball call, you’re almost certainly not alone. And the referee might be right there alongside you. The application of the rule often doesn’t align with the letter of the law.

Oh, and two final notes:

• Goalkeepers are allowed to use their hands in the penalty box. Outside it, handball rules apply to them just like they do to all other players.

• The one other situation in which a keeper may not handle the ball is when a teammate passes it back to him with his feet. A goalkeeper may, however, handle the ball if the back-pass is a header.

The card system

Why do refs reach for their pockets and brandish colored cards? The origin story actually involves a traffic light. As the inventor of the card system, Ken Aston, says of his attempts to develop a tiered, cautionary punishment system: “As I drove down Kensington High Street, the traffic light turned red. I thought, ‘Yellow, take it easy; red, stop, you’re off.'”

There you have it. Red cards are what American sports refer to as ejections. Yellow cards are the in-between. If a player receives two yellows in the same game, a red accompanies the second one.

And there’s one key difference from American sports ejections. If a player sees red, his or her team must play the rest of the game 10-on-11.

So what types of fouls draw yellow and red cards?

Yellows are handed out in cases of delay of game, dissent, unsportsmanlike behavior, excessive celebration and “simulation” – also known as diving or flopping. They’re also for reckless tackles and fouls that halt a promising attack, or for an accumulation of fouls – for persistent infringement by a single individual.

Red card offenses include, but are not limited to, “serious foul play,” the denying of an obvious goalscoring opportunity (DOGSO), “violent conduct,” offensive gestures or language, biting, and spitting at someone. All of these are further defined in the rulebook. But again, many require subjective judgement.

Some other notes:

• If a player commits a foul and denies an obvious goalscoring opportunity in the penalty box, and if the player made a genuine attempt to play the ball, the DOGSO provision gets overruled. The attacking team gets the penalty kick, but the player only receives a yellow card, not a red.

• A referee can play advantage on a yellow card foul, then wait until the next stoppage to go back and issue the yellow.

• The laws of the game specifically state that the following should not be the case, but referees often raise the yellow card threshold if a player is already on a yellow – and, therefore, if another yellow would bring out a red.

• Yes, Cristiano, taking your shirt off still fits the “excessive celebration” description, and is going to get you a yellow.

Video review

For the first time at a World Cup, video review – commonly known as VAR – will be in use in Russia. FIFA has unveiled extensive plans, including four video assistant referees and 35 cameras per match. You can read more here, and watch more below.

In short, here’s what you need to know:

• Video review can be used to either overturn or award goals, penalty kicks or red cards. The fourth category is cases of mistaken identity – when, say, a yellow card is awarded to the wrong player. But VAR cannot be used to overturn or award yellow cards, common fouls, corner kicks and so on – unless, for example, the lack of a foul call led directly to a goal or penalty.

• For a foul decision to be reversed, the review must determine that the referee’s on-field error was “clear and obvious.”

• “Clear and obvious” is not a requirement for the reversal of offside decisions, however.

• In most cases, referees will simply put their hand to their ear and listen to the video assistant; in others – laid out here – they have the ability to go to sideline monitors and re-watch the play themselves.

Unwritten rules

Soccer is full of quirky customs. But the one unwritten rule to know concerns injuries.

If a player crumples to the turf in pain, referees are only required to stop games in the case of a suspected head injury. Otherwise, the stricken player is ignored. But proper etiquette is for the team with the ball to kick it out of bounds to allow the injured player to get treatment. Once he’s up and off the field, the ball is then thrown in and kicked back to the team originally in possession, and play resumes from the back.

There are certainly exceptions, though. Not everybody will kick the ball out, especially if there is suspicion that the player is faking the injury. And very rarely will a player dispose of the ball if an opponent goes down injured during a counterattack.

This, of course, leads to disputes, when teammates of the injured player expect the ball to be put out of play, but the possessing team doesn’t oblige. And what if a player under pressure kicks the ball out of bounds, playing the sportsmanship card, but with the hidden motive of a lack of passing options?

Like so much in soccer, there are gray areas. You’ll learn as you go. The controversies and unending debates are part of the sport’s beauty.

More Soccer for Dummies: Part 1 (Terminology) | Part 3 (Tactics)

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Henry Bushnell covers global soccer for Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com, or follow him on Twitter @HenryBushnell, and on Facebook.

World Cup coverage from Yahoo Sports:
• 2018 World Cup preview hub
• How Mexico is wooing another type of dual national: fans
• From Messi to Henderson, the top 100 players at the World Cup
• Group previews: A | B | C | D | E | F | G | H