In rugby union, what shirt number gives its name to a playing position?

In the game of rugby union, there are 15 players on each team, comprising eight forwards (wearing jerseys numbered 1–8) and seven backs (numbered 9–15). In addition, there may be up to eight replacement players "on the bench", numbered 16–23. Players are not restricted to a single position, although they generally specialise in just one or two that suit their skills and body types. Players that play multiple positions are called "utility players".

The number eight, or eighthman in South Africa, binds between the locks at the back of the scrum, providing extra weight at the push. Number eights interact with the scrum-half at the back of the scrum to control and provide clean ball for the backs. They can also pick the ball from the back of the scrum and run with it or pass it to the scrum-half. At line-outs, they can be either another jumper or a lifter. Around the field, they have a similar set of responsibilities as the flankers at the breakdown. Number eights are often strong ball carriers and run off the backs in an attempt to break through or push past the opposition's defensive line.