They are the men who plot their side's course through a match. The scrum half and fly half, No. 9 and No. 10 or, if you're a New Zealander, a first five-eighth.
The half-backs provide the brains to the brawn smashing lumps out of each other all around them.
Their performances, above all others, can determine the outcome of a contest, and when their understanding is on a par with the 10 pairs we look at here, they can propel their sides to great heights.