Scrum, flanker, prop, and full-back are words used in which sport?

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".

Forwards compete for the ball in scrums and line-outs and are generally bigger and stronger than the backs. Props push in the scrums, while the hooker tries to secure the ball for their team by "hooking" it back with their heel. The hooker is also the one who is responsible for throwing the ball in at line-outs, where it is mostly competed for by the locks, who are generally the tallest players on the team. The flankers and number eight are expected to be the first players to arrive at a breakdown and play an important role in securing possession of the ball for their team.

The backs play behind the forwards and are usually more lightly built and faster. Successful backs are skilful at passing and kicking. Full-backs need to be good defenders and kickers, and have the ability to catch a kicked ball.