William Zillman has had to fight off a challenge from fellow Titan David Mead to maintain his position as the side's first-choice fullback. Credit: Charles Knight. Copyright: NRL Photos
Any person with a basic understanding of mathematical properties will tell you that it is impossible to have more than two halves but the evolution of the rugby league fullback puts that theory to the test.
In a blessed age for the custodians of rugby league teams, naming the No.1 No.1 is as difficult a task as naming the best chocolate in a box of Cadbury Roses; it's all a matter of personal preference.
While many will vouch for the power of a Greg Inglis others will espouse the virtues of speed men such as Billy Slater but talk to an Eels fan and they will proudly tell you that their man is blessed to have both.
Whereas the great fullbacks of the past were lauded for their support play, proficiency under the high ball and an ability to test the line on kick returns, today's fullbacks must do all that in addition to acting as an integral cog of the attacking machine.
In other words, he must become the third half.
It's an evolution that Titans fullback William Zillman has had to continually adapt to over his nine seasons in the NRL and ahead of a match-up with Sea Eagles superstar Brett Stewart at Cbus Super Stadium on Sunday, says it is that presence in attack that has been the biggest change.
"The way the game is these days there's not necessarily a first and second receiver. Both the halves work a side each so as a fullback you need to be able to play both sides and communicate with each of your halves to know which way the ball's going," Zillman said.
"It's not a case of the same first receiver always being the halfback then the five-eighth and the fullback's out the back, it's fairly different now.
"You'll see a lot of fullbacks go first receiver, a lot of fullbacks go second receiver and when you're playing from the middle of the field you need to know which side you're going. So the hardest thing is knowing what your halfbacks are going to do and playing off the back of that.
"There is a lot more asked of the fullbacks these days; most teams tend to consider them as a third half so you'll notice a lot of fullbacks have really good kicking games and contribute to kicks, passing games so there's a lot more involvement than in past years.
"There are a lot of similarities now between [halfbacks and fullbacks] but the most important thing is that they can work together."
Outside of the hookers and the halves, the fullbacks get their hands on the footy more often than any other player on the field with Penrith's rising star Matthew Moylan topping the possession count of the No.1s with 811.
Of the fullbacks to have played at least five games at the back in season 2014 Jarryd Hayne is far and away the leading try-scorer with 17 and has six more line breaks than Canberra's Anthony Milford. Milford's 24 offloads are four more than the next best in Moylan, Brett Stewart's 20 try assists compare favourably with the game's premier playmakers while Ben Barba's 17 try saves are the most of any player in the competition.
Milford and Anthony Minichiello are the experts at defusing bombs while when it comes to making metres on kick return Minichiello and Inglis are the only two to have busted through the 1000-metre mark through 22 rounds.
And don't get me started on Michael Morgan's all-round capabilities after one season as the Cowboys' No.1.
Rather than jack-of-all-trades they are expected to be masters of all and the result of any particular game often hinges on their input at both the offensive and defensive ends of the field.
Even asking an experienced campaigner such as Zillman to name the opposition fullbacks he most admires ends up being a roll call of the first names on the team sheet each week.
"Brett Stewart is definitely one, Billy Slater... There are so many good fullbacks these days, that's the thing, they're all superstars," said the veteran of 142 first grade games. "There's Greg Inglis and Jarryd Hayne, there are plenty of good ones running around so plenty of guys for me to look at and pick some tips up from."