UFC 205 fight week has arrived in New York City as 26 fighters prepare for one of the biggest nights in mixed martial history inside Madison Square Garden on Saturday, Nov. 12.

As the UFC hosts its first event in New York since the 19-year ban was lifted last March, thousands of MMA fans will be plugged in to the events of the week. With more than 20,000 people expected at MSG for UFC 205, and millions of dollars being spent on tickets, restaurants, bars, etc., the spectacle of a big event in New York undoubtedly will attract a few new sets of eyes.

So for those new folks interested in how it all works, here’s a primer on what MMA is, who the UFC is and what the heck will be going on inside “The World’s Most Famous Arena” on Saturday.

The sport is called mixed martial arts, or MMA for short. UFC is the acronym for Ultimate Fighting Championship, the largest mixed martial arts promotion in the world, with its main competition being Bellator and World Series of Fighting. Fighters don’t “train UFC.” They train for MMA, and the UFC is a company they fight in. Not unlike how basketball is a sport and the NBA is a league.

Mixed martial arts draws from various disciplines such as boxing, wrestling, jiu-jitsu, taekwondo, judo, kickboxing, Muay Thai and karate. Each of the sports that comprise mixed martial arts has been legal to compete in professionally in New York State for years. Only the combination of them in the form of MMA was banned in New York from February 1997 until March 2016.

A bout can end in one of several ways: knockout, technical knockout, submission, doctor’s stoppage, judges’ decision (unanimous, majority, split), draw or disqualification.

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Championship fights and fights scheduled for the main event of a fight card are five-round bouts. All other fights are three rounds. Each round lasts five minutes.

An MMA event and the fighters on the card are governed and regulated by the athletic commission of the host state. Certain rules and regulations can vary from state to state, but there is a unified set of rules for MMA that serve as a guideline.

Three judges score the bout cageside on a 10-point must system, similar to boxing. One notable difference is that in boxing, if there’s a knockdown, it’s almost always scored a 10-8 round. In MMA, the standard for a 10-8 round is far higher.

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The UFC has eight weight classes for men’s MMA: Flyweight (125 pounds), Bantamweight (135), Featherweight (145), Lightweight (155), Welterweight (170), Middleweight (185), Light heavyweight (205) and Heavyweight (up to 265).

The UFC has two weight classes for women’s MMA: Strawweight (115 pounds) and Bantamweight (135).

Fighters weigh in the day before the scheduled bout. The UFC uses what are known as “early weigh-ins,” which gives fighters a two-hour window in the morning to make weight. Prior to the early weigh-in process recommended by the California State Athletic Commission and first used in June 2016, fighters weighed in during the half-hour weigh-in show usually at 4 or 5 p.m. local time.

Fighters in non-championship bouts are given a one-pound allowance over the limit. Championship fighters are not afforded the one-pound allowance. Any fighter who misses weight forfeits 20 percent of their fight purse, and the bout is contested at a catchweight. In certain instances, a fighter can be fined a higher percentage and the bout also could be canceled.

Contrary to the marketing slogans used in the original days of the UFC back in the 1990s, there actually are rules. (There were back then, as well, too.) The following acts are considered fouls and could result in point deductions or disqualification:

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Butting with the head

Eye gouging of any kind

Biting

Spitting at an opponent

Hair pulling

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Fish hooking

Groin attacks of any kind

Putting a finger into any orifice or any cut or laceration of an opponent

Small joint manipulation

Striking downward using the point of the elbow

Striking to the spine or the back of the head

Kicking to the kidney with a heel

Throat strikes of any kind, including, without limitation, grabbing the trachea

Clawing, pinching or twisting the flesh

Grabbing the clavicle

Kicking the head of a grounded opponent

Kneeing the head of a grounded opponent

Stomping a grounded opponent

Holding the fence

Holding the shorts or gloves of an opponent

Using abusive language in fenced ring/fighting area

Engaging in any unsportsmanlike conduct that causes injury to an opponent

Attacking an opponent on or during the break

Attacking an opponent who is under the care of the referee

Attacking an opponent after the bell has sounded the end of the round

Timidity, including, without limitation, avoiding contact with an opponent, intentionally or consistently dropping the mouthpiece or faking an injury

Throwing opponent out of ring/fighting area

Flagrantly disregarding the instructions of the referee

Spiking an opponent to the canvas on his head or neck

Interference by the corner

Applying any foreign substance to the hair or body to gain an advantage