In the game of rugby union, there are 15 players on each team, comprising eight forwards (numbered 1–8) and seven backs (numbered 9–15). In addition, there may be up to eight replacement players "on the bench". Jersey numbers 16–23 differentiate them. Players are not restricted to any single position on the field, although they generally specialise in just one or two that suit their skills and body types. Players that specialise in over three positions are called "utility players". The scrum (an assemblage used to restart play), however, must consist of eight players: the "front row" (two props, a loosehead and tighthead, and a hooker), the "second row" (two locks), and a "back row" (two flankers, and a number 8). The players outside the scrum are called "the backs": scrum-half, fly-half, two centres (inside and outside), two wings, and a fullback. Early names, such as "three-quarters" (for the wings and centres) and "outside-halves" (for fly-half) are still used by many in the Northern Hemisphere, while in the Southern Hemisphere the fly-half and inside centre are colloquially called "first five-eighth" and "second five-eighth" respectively, while the scrum-half is known as the "half-back".