Ten months ago, Jarryd Hayne tearfully announced he was leaving Parramatta and the NRL to chase his dream of a new career in the NFL.

A poll at the time on the ABC Grandstand site showed 55.9 per cent of people thought he would not succeed.

This year, Hayne signed a $US100,000 contract with the San Francisco 49ers, but his chances of making an NFL career still looked like a shot in the dark for the Australian sporting household name.

But this month, as the former State of Origin star played his first two preseason games for the Niners, the 27-year-old has made believers of a lot of people.

His brilliant punt returns and long gains running the ball have kickstarted a growing highlight reel that shows no sign of stopping.

For many Australian sports fans, however, the game Hayne is trying to crack is a mystery stop-start affair, with odd positions and confusing rules.

Use these links to check out Grandstand's guide to American football: The Game

The Game Scoring

Scoring Positions

Positions Penalties

Penalties Turnovers

Turnovers Timing

The Game

Every play in American football starts like this, with the two teams setting themselves for action on opposite sides of the line of scrimmage. ( Scott Halleran: Getty Images )

American football is played on a rectangular field that is 100-yards (91.4m) long and 53.33 yards (48.9m) wide.

At either end of the field are end zones (like rugby league's in-goal area) that are the same width and 10 yards (9.14m) deep.

At the back of the end zone are goal posts - the object of the game is to keep possession and move - or drive - the ball downfield to score in a variety of ways.

In rugby league, possession is measured in tackles - in the NFL, it is measured in downs.

Before each play or down, the ball is spotted on the ground - known as the line of scrimmage - where both teams line up opposite each other before the start of the play.

Teams have four downs to move the ball 10 yards. If successful, they earn a first down - another four downs to go another 10 yards and so on.

If teams with the ball do not make the 10 yards by the end of third down, however, they usually kick the ball away - either a punt, which gives the ball back to their opposition, or an attempted field goal, where they try to kick the ball through the posts at their opponents' end to score three points.

Examples of the terminology are: "1st and 10" (first down with 10 yards to go for another first down; "2nd and four" (second down with four yards to go for a first down), "3rd and five" (third down with five yards to go for a first down.

This changes when the ball is 10 yards or less from the end zone on offence (the attacking team).

If a team makes a first down on their opponent's eight yard line, it becomes "1st and goal" from the eight-yard line, then "2nd and goal," 3rd and goal" and 4th and goal", regardless of whether the ball remains inside the 10-yard line or goes backwards.

Scoring

Even if a defender managed to stop Pierre Thomas hitting the ground in the end zone it would still be a touchdown, because he has already "broken the plane" of the goal-line. ( Scott Boehm: Getty Images )

The most well-known scoring option in American football is running or passing the ball into the end zone for a touchdown (worth six points).

This name is a misnomer, however, because you do not need to touch the ball down to score, merely "break the plane" of the goal-line - think of an imaginary extension of the goal-line that goes directly upwards.

So a player can be on, above or behind the plane, but if some part of the ball passes over or through the plane and over or inside the pylon (like the corner-flag) at the four points of the end zone, a touchdown is scored.

Following a touchdown, teams can opt for a one or two-point conversion. Kicking an extra point is worth one point, while running or passing the ball into the end zone from two yards out is worth two.

Touchdowns can be scored by the offence, the defence or by Jarryd Hayne's likely home, special teams (the ones who take or cover kick-offs or punts).

Aside from a field goal, the other alternative is to score a safety, worth two points, where the defence tackles the ball carrier inside the offence's end zone.

Normally when a team scores, they kick the ball off afterwards from their own 35-yard-line, but following a safety, the team that conceded the safety has to kick off from their own 20-yard line.

Positions

Part of the mystery of American football is the unfamiliar position names.

Offence

Wide receivers are among the most high-profile players in the NFL, but they often have to work very hard for the ball. ( Donald Miralle: Getty Images )

The most well-known is that of quarterback, the most important player on offence.

He calls the play before it happens, takes the ball on each play and usually throws it to a pass-catching wide receiver, tight end or running back, or hands off to a running back to run with the ball.

Some quarterbacks, like San Francisco's Colin Kaepernick, are known for their ability to gain yards running (or rushing) with the ball, and they can take defences by surprise.

In order to make space for players to gain yards, the offensive line - made up of the centre, left and right offensive guards and offensive tackles - stands in front of the quarterback and blocks (or shepherds) for the attacking player, by using their bodies to stop the defence from getting to the quarterback or running back.

The centre is the player who starts every play by snapping the ball (throwing it between his legs) back to the quarterback, the punter or the kicker.

Running backs' main role is to run or rush the ball to gain yards - in Jarryd Hayne's first two NFL games he has taken advantage of blocking and used his own evasive skills to produce rushes of 53 and 34 yards.

Running backs and tight ends also block, depending on their roles on a play.

Tight ends and wide receivers' main role is to catch passes from the quarterback - wide receivers are usually the fastest men on the offence and are often capable of making spectacular plays.

Defence

Even the best quarterbacks - like Tom Brady of the New England Patriots - get caught and sacked by the defense sometimes. ( Donald Miralle: Getty Images )

The first line of defence is called the defensive line, made up of defensive ends and defensive tackles.

Their job is largely to stop opposition runners gaining yards with the ball, and to sack the quarterback - tackle him behind the line of scrimmage - if they can.

Next are the linebackers, who call plays and lead the defence. They are either middle or outside linebackers, depending on where they line up on the field.

Furthest from the line of scrimmage are the defensive backfield - sometimes known as the secondary - made up of cornerbacks and safeties.

Their job is to stop the offence completing passes, or to stop wide receivers, tight ends and running backs making yards after they catch the ball.

An even better result is if they can intercept the pass and get the ball back for their team.

Special teams

The goal as a punt returner? Don't lose the ball, make the tacklers miss and gain as many yards as you can. ( Getty Images: Brian Bahr )

Finally, we have special teams, the section where Jarryd Hayne has excelled so far.

Special teams include coverage players for kicks - punts and kick-offs - and long snappers, who are used to snap the ball back to punters and kickers.

Hayne's abilities fit the mould of the punt returner or kick returner, whose job it is to field punts or kick-offs from the opposition and run them back up the field, gaining as many yards as possible to give their team's top field position.

Hayne's speed and his ability to step repeatedly and evade tacklers make him an ideal return man - against Dallas he averaged 28 yards per punt return, where anything averaging over nine yards is considered good.

Penalties

A pass interference call against either side can result in a big change in field position for the team in possession. ( Getty Images: Al Messerschmidt )

American football has a long list of rules, some of them obscure, others for everyday situations. Penalties are signalled by umpires throwing a flag at the spot of the foul.

The most commonly called penalties are for offensive and defensive holding, false starts, pass interference and unnecessary roughness.

You can check out a list of penalties and the umpires' signals here.

Holding:

On offence you can use your body to leverage a player out of the way or keep them getting to the ball. But you are not allowed to grab the player with your hands or arms. The ball is moved back 10 yards, so 1st and 10 becomes 1st and 20, for example.

On defence, the defender cannot illegally restrain a player who does not have the ball. The penalty is five yards, but here the ball is moved forward and it is an automatic first down.

False start:

Any offensive player who - prior to the snap of the ball - makes a sudden movement towards the line of scrimmage to simulate the start of the play, commits a false start. The penalty is called before the play starts, and the ball is brought back five yards - 1st and 10 becomes 1st and 15.

Pass interference:

This is one of the most controversial calls, because umpires are sometimes more lenient than others and also the size of the penalty can have a big impact on the game. A defender who makes intentional physical contact with a receiver after the ball is thrown to prevent or hinder the player from catching the ball, has interfered with the play. The ball is moved to the spot of the foul - if the foul is in the end zone the ball is moved to the one-yard line. Automatic first down.

If an offensive player makes intentional contact with a defender after the snap to prevent him catching a ball, it is also pass interference. This takes a 10-yard penalty.

Unnecessary roughness

In a hard-hitting game like the NFL, players sometimes cross the line, such as hitting a ball carrier after he is out of bounds, or making a heavy hit "piling on" on a player who is already down.

The penalty is 15 yards, and an automatic first down if committed by the defence.

An important note is that a team can refuse or decline penalties - for example, if a team scores a touchdown on a play it will decline a holding penalty that would only result in a gain of five yards.

Turnovers

Intercepting a pass from the quarterback can change the whole momentum of an NFL game. ( Getty Images: Ronald Martinez )

Turnovers of possession are crucial in American football - because they are much more rare than in rugby union, rugby league or AFL, they usually change the momentum of the game when they occur.

Turnovers come in two forms - fumbles, or interceptions.

A fumble happens when a player with the ball is hit and the ball is knocked free before his knee touches the ground, ruling the play complete.

If the fumble is recovered on the ground by the defence, that team immediately takes over at the spot of the fumble with the chance to go into attack on offence.

The fumble can be returned, however, and if the defender with the ball is not tackled, he can go all the way for a touchdown.

The same happens with an interception, when a pass is thrown but the ball is caught by a defender before it touches the ground.

Interceptions can also be returned for touchdowns.

Timing

Teams who are leading love being able to "take a knee", running out the clock to win the game. ( Getty Images: Norm Hall )

Games are played in four quarters, each containing 15 minutes of game time.

However the clock stops every time the ball goes out of bounds and every time a pass hits the ground - ruled an incomplete pass.

There is a 45-second maximum time between the end of one play and the start of another if the ball remains in bounds.

Each team also gets three time-outs in each half, and there are scheduled breaks at the end of each quarter and at the "two-minute warning", when two minutes of game time remain in each half.

This is the reason American football can frustrate Australian viewers, as one hour of game time extends to three hours or more of real time.

When teams are leading late in the fourth quarter, they will tend to try to "run out the clock".

This means running the ball and keeping it within bounds, which forces the defence to use their time-outs to stop the clock.

Once the defence uses all its time-outs, offences can line up and wait until the last second (literally) to snap the ball.

If there is less than 45 seconds left in the game, and the other side has no time-outs, the offence can effectively end the game by "taking a knee".

The quarterback grabs the snap and kneels down, ruling the play complete as the clock runs out.