Originally there were only two Rugby Positions - forwards and backs.
It was only when the rules were first drafted in the 1870's that the
full back, of which there were three, was named and his role defined.
A rule change limited the position to one player on the rugby field
for each team. The decision was then made that the other two players
would be stationed at a midpoint between the forwards and the full
backs and were to be called halfway backs. In time this was shortened
to half backs. Their role and that of the full back continued to be in
position to fall on the ball in the event of the opposition hacking it
out of the scrum.
In 1878 at Cardiff, in Wales, they developed a short pass to one of
the half backs who would then go charging ahead with the ball. He
became known as the flying half back which in time was shortened to
the fly half.
In addition they reorganised the scrum, developed short passes amongst
the forwards and long passes amongst the backs. This lead to the need
for more players to be placed in the back line between the halves and
the full back so they were called quarters and the fact that three of
them were put in this position led to them being known as "three -
quarters". The middle player being called the centre with the two on
his outside called wings.
The introduction of a fourth player into the three-quarters was to a
large extent, accidental, with Wales again being allowed to take the
honour. Cardiff were due to play a tough match away from home and
their first choice centre was not available so they promoted one Frank
Hancock from the second side in his place. Hancock was a great success
scoring two vital tries. When the Cardiff selectors sat down to pick
their team for the next match they were keen to revert to their
original team, but they were most reluctant to drop Hancock, so they
compromised by introducing a fourth three-quarter. Within two years
Wales had introduced it at international level and the game became
closer in postions to today.
The New Zealanders were quick to see the advantage of having a fourth
player in the three-quarters. Their solution was to change the
standard rugby positions by pulling a forward out of the pack and put
him between the half back and the three-quarters. Their problem was
what did they call the new position. Legend has it that consent was
reached by deciding that the half back was 4/8ths and the
three-quarters 6/8ths, so therefore the new position must be a 5/8ths,
a name that has continued to this day in that country. When fly half
play developed they introduced the first 5/8th and the second 5/8th.