1 & 3 Props
Props are pillars of the scrum, supporting their hooker, and key lifters in the lineout. Designated as
loosehead (wears No. 1 jersey) and tighthead (No. 3 jersey), the props must be strong and technically sound.
Due to their size and strength, props are used to rip the ball free in mauls and run with the ball in
pack-driven offensive play.
The hooker (wears No. 2 jersey) gets his/her name from the action of "hooking" the ball back to his teammates in the scrum play. Generally, it is the hooker that throws in the ball at a lineout. Hookers must be mobile, have good speed, and be a reliable tackler.
4 & 5 Locks
Locks are generally the tallest individuals on the team with superb leg strength. A lock (wears No. 4 or 5 jersey) may support a jumper or be one himself in the lineouts, but their most important function is in the scrum. Most of the forward push in a scrum is generated within the second row.
6 & 7 Flankers
The flankers (wear No. 6 or 7 jersey) bind in at the side of the scrum. The primary tasks of the flanker are to win the ball in loose play, support a jumper or be one himself in the lineouts, and be an excellent tackler. It is often the flanker that provide the crowd with exciting and wincing defensive plays.
The "8-Man" (you guessed...wears No. 8 jersey) packs down at the back of the scrum, between the two locks. The 8-Man is responsible for presenting the scrum-half with a good ball from the scrum, or sometimes launching an offensive from his/her position. The 8-Man needs to be physically imposing with a good balance of skills.
The scrum-half (wears No. 9 jersey) is responsible for feeding the ball into the scrum and dispensing the ball to forwards or backs for an offensive attack. The scrum-half is an aggressive player with excellent ball handling skills. The scrum-half often tangles with the forwards, so they tend to be tough, resilient rugby players.
The fly half (wears No. 10 jersey) is generally they key decision maker who decides to either distribute the ball to the backs or kick for better position. He/she should have a good range of skills with the ball in hand or off the foot. Fly halves are methodical, elusive runners with a knack for setting up their fellow backs for big offensive plays.
12 Inside Center
The primary role of the inside center (wears No. 12 jersey) is to knock holes in the opponent's defense and has the primary defensive role in attacks against his/her own back line. Inside centers usually pound the ball into the opponent's defense, despite their desire for stealthy, slashing runs.
13 Outside Center
An outside center (wears No. 13 jersey) generally has more pace than power, as compared to his inside center. The outside center must be able to make holes in the opponent's defense, but also exploit the gaps made by the movements of his/her teammates. If the outside center can't bust through; he/she has a wing on the outside to pass the ball to.
11 & 14 Wings
Wings (wear No. 11 or 14 jersey) are generally the fastest players on the team, whose primary function is to get the ball and sprint for the goal line. Often wings are called upon to field an opponent's kick and retrieve the ball when done so by his/her team. Historically, wings were small, fast players. In modern rugby, wings have gotten significantly larger to both speed past defenders and break through multiple tacklers.
The fullback (wears No. 15 jersey) is the last line of defense against a running attack and the opponent's tactical kicks. The fullback must be able to cleanly field an opponent's high, hanging kick while being unconcerned about the prospect of being gang-tackled when he/she fields the ball. The fullback must have a balanced set of skills; he/she may enter the attacking back-line to overload a side or provide tactical kicks to prevent an opponent's score.