Two packs of players, straining every muscle for every inch of opposition territory they can claim.
Of course, it's the scrum.
It is used for restarting play after the following:
The ball has been knocked on
The ball has gone forward
The ball has not come out from a ruck or maul
Not every player can join a scrum. Only eight players from each team can take part.
They are almost always the eight forwards in the side.
The scrum is formed at the place where the infringement happened.
All scrums must take place at least five metres from the touch or trylines.
However the scrum is one of the hardest areas of the game to referee because of the many infringements, particularly in the front row.
Referees pay particular attention to the bindings of the two front rows.
Props must use the whole arm from hand to shoulder to grasp their opponent's body at or below the level of the armpit.
They must grasp their opposite number's shirt from the side or the back.
They cannot go underneath and grab the collar or the sleeve of the upper arm.
Props often look for a late bind when they engage.
By maneuvering their arm they can manipulate their opponent's body position, giving them a significant advantage in the push.
However referees are stringent on this move because of safety reasons.
Twisting, dipping or collapsing a scrum will result in a penalty against the offending team.
FRONT ROW OFFENCES
Rather than engaging square on with their opponent, tight-head props can bore their heads into the hooker.
This limits the movement of the opposition hooker.
Sometimes you may see a tight-head prop's body pop out of a scrum while it is still taking place.
This is because their opposing loose-head prop has used a subtle shift of body position and pushed into the tight-head prop's chest.
Both moves are illegal and are punishable with penalties.