Positions
Backs
15. Fullback
The full back stands back to cover defensive options as a 'sweeper' behind the main line of defence removed from the other backs. As the last line of defence, they require good tackling skills.
14. and 11. Wing
Wingers often act as additional full backs on opposition kicks. In addition to this responsibility, they must get back from an opposition kick to give the full back options on either side. The modern game means that the back three tend to act as a unit in fielding kicks and counterattacking, rather than all responsibility lying with the full back. Wingers need to have all the skills of a full back, though the emphasis would be on attack rather than defence. As such, many players are as competent on the wing as at full back.
A common tactic is to have the winger receive the ball and then cut towards the centre of the pitch. This changes the direction of play, which may catch the opposition off guard, or may create space for the outside centre to receive a switch pass or "scissors pass".
13. Outside centre & 12. Inside centre
Centres need to have a strong all-round game: they need to be able to break through opposition lines and pass the ball accurately. When attack turns into defence they need to be strong in the tackle. Usually the two centres are divided into outside centre and inside centre, though sometimes teams play with left and right centres.
The outside is typically the heavier, more powerful of the two centres. They are the "rapiers" that are given the ball, normally via the fly half, or inside centre to make breaks through the opposition backs before offloading to the wingers after drawing the last line of defence. Good size and tackle breaking skills are very important for outside centres to have. They may also need to be very aggressive in defense, espescially when a team is using a rush up style defense.
The inside centre tends to be the smaller of the two centres. In defence or attack, the inside centre is always in the thick of the action, drawing the opposition's defence, making the breaks to make the space for the outside centre and dishing out the tackles in defence along with the forwards. Some of the skills of the fly-half, such as distribution and kicking, can be advantageous to inside centres, as they may be expected to act as fly-halves if the normal fly-half is involved in a ruck or maul.
10. Fly-half
Games are rarely won on tries alone, and a fly-half who is also the goal kicker (which is often the case) can be the most important player in the side.
9. Scrum-half
Scrum halves form the all-important link between the forwards and the backs, and are invariably at the centre of the action. A scrum half is normally relatively small but with a high degree of vision, the ability to react to situations very quickly, and good handling skills.
Forwards
1. Loosehead prop & 3. Tighthead prop
The laws of the game require the tighthead prop to bind with his or her right arm outside the left upper arm of his opposing loosehead prop and similarly they restrict what the loosehead prop can do with his left arm. Although the scrum half may put the ball in on either side of the scrum, he is unlikely to choose the tighthead side because otherwise the opposing hooker would be between him or her and his or her own hooker. Hence, the laws implicitly require the loosehead prop to be on the left side of the scrum.
Props are also in the position of being able to direct the movement of the scrum in moving side to side to prevent the other teams scrum from "wheeling" the set scrum and forcing another "put in" from the opposing side.
2. Hooker
4. & 5. Lock
Locks are very tall, athletic and have an excellent standing jump along with good strength. They also make good ball carriers, bashing holes in the defence around the ruck and maul. They also have to push the rucks and mauls and are the main figures of rucks and mauls.
6. Blindside flanker & 7. Openside flanker
In open play, flankers will often stand behind the back line 'supporting' them in open play. If any ball is dropped by the backs, the flankers job is to clear up messy ball and take it ito contact to start a fresh and new phase of play. Because they are always close to the ball, they are often first to the break down.
Flankers usually protect scrum-halves during scrummages from the opposing scrum-half following around and tackling him/her.
Since most of the back play is usually on the open side, where there is more space, it is usually the openside flanker's job to be the first to any breakdown of play and to get his/her hands on any loose ball (or to cause a breakdown by tackling the ball carrier or otherwise harrying him into error). At a scrum where the ball has been won by the opposition, the openside flanker often has the best view of when the ball is out and is able to break away and close down the opposing ball-carrier, reducing the time available for a pass or kick. Openside flankers are often smaller, faster and more mobile than their blindside counterparts.
8. Number eight
Number eight is the only position that does not have a specific name and is simply referred to as 'the number eight'. The modern number eight has the physical strength of a forward along with the mobility of other loose forwards. The number eight packs down at the rear of the scrum, controlling the movement of the ball to the scrum-half with his/her feet. The number 8 is the position where the ball enters the backline from the scrum and, hence, both fly half and inside centre take their role from the number 8 who as the hindmost player in the scrum can elect to pick and run with the ball like a back. As a result, the number 8 has the opportunities as a back to run from set plays.
They are normally tall and athletic and used as an option to win the ball from the back of the lineout. Like flankers they do less of the pushing than locks or props, but need to be quick to cover opposition half-backs. A number eight should be a key ball winner in broken play, and occasionally a 'battering ram' at the front of rucks.