WHEN Nathan Brown went down with a ruptured anterior cruciate ligament in his left knee at training on Monday, Collingwood’s hopes of going back-to-back certainly didn’t go down with him.

The loss of the 22-year-old key defender - Nick Riewoldt’s nemesis in last year’s Grand Finals - will no doubt hurt the Magpies, but not as much some might expect.

When assessing how Brown’s absence will affect the Pies, it’s important to recall that before his Grand Final heroics, the strong-bodied left-footer had been viewed as the logical successor to veteran Simon Prestigiacomo and was simply biding his time until the old full-back hung up his boots.

Consequently, Brown was overlooked for much of last season as the Pies preferred Prestigiacomo and the emerging Ben Reid (who was taken by the Pies at No.8, two places ahead of Brown, in the 2006 NAB AFL Draft) in the key defensive posts, with Brown playing just five AFL games in the opening 17 rounds.

Admittedly, he missed three games (rounds 13-15) with a shoulder problem, but he was named an emergency just twice in that period.

It was only when Reid and then Prestigiacomo were sidelined with injury that he finally gained some continuity by playing the last seven games of the season.

Brown was, of course, extremely lucky to play in the Grand Finals after being a late inclusion for Prestigiacomo, who had suffered a groin injury, but more than justified his selection with wonderful jobs on Riewoldt, who some Pies fans have playfully referred to as, among other things, ‘Browny’s Bunny’.

In light of Prestigiacomo’s retirement, and despite the return of Chris Tarrant, the consensus view was that Brown would gain such confidence and stature from his finish to 2010 that he would become a permanent - or at least regular - member of the Pies’ backline.

Brown’s emergence had engineered a seamless, and enviable, succession plan in defence. He’d awaited his opportunity and, at long last, it had materialised.

In the process, the Pies had the luxury of boasting two big, young, strapping defensive pillars (Reid, of course, being the other) to shoulder the heavy ‘gorilla’ work in the back half for the much of next decade as the club embarks on what it hopes is the beginning of a dynasty.

Establishing a strong, cohesive, tight-knit back six is often regarded as the first prerequisite to success, and it’s a philosophy to which Collingwood coach Mick Malthouse has always subscribed, building his teams around a settled backline and broader team defence. This celebrated Collingwood line-up is no exception.

The Pies’ back six was well and truly settled. Reid and Brown were the two talls, skipper Nick Maxwell and Harry O’Brien were the medium-sized playmakers who could also play tall or small, Heath Shaw and Ben Johnson would alternate between dashing defensive and midfield roles, while Alan Toovey, the lockdown runner, was the other constant in the back half.

Prized recruit Chris Tarrant was to be the cream on top to bolster the defensive and forward zones on a needs basis.

But AFL football often throws up the unexpected and tests the most comprehensive contingency plans.

For Brown, the highest of peaks has been swiftly followed by the lowest of lows, and he now faces a physical and mental battle to return to the playing field for 2012.

At least he has the counsel of a close confidante who has been through it all - his twin brother Mitch, who underwent a knee reconstruction with West Coast after tearing his ACL in the 2008 pre-season and has made reasonable progress since.

The Pies will be hoping Brown makes a similar recovery, but the seriousness of such injuries generally dictates that it takes some time for the returning player to adapt to the tempo and movement requirements of the game, let alone regaining their pre-operation form.

With Brown out of the equation, Tarrant appears his most logical replacement, and most observers would say the Pies don’t lose anything in that exchange; in fact, they probably gain a bit because Tarrant is faster, stronger, more experienced and, at his best, an All Australian candidate with a good record on most of the game’s biggest and best forwards.

But it might also be a classic rob-Peter-to-pay-Paul scenario, with Tarrant’s influence as a utility (or ‘swingman’ in modern parlance) drastically reduced to an almost permanent defensive role.

That would not only disappoint Malthouse but also Pies fans who had hoped to see Tarrant unleashed for regular play in attack, where his lightning leads and occasional sky-scraping marks made him a great asset in his first stint at the club.

Another beauty of the Pies at the moment is that they are also well-endowed with attacking options, although an injury to key forwards Travis Cloke or Chris Dawes would force a rethink of Tarrant’s role and might have him once again kicking goals rather than saving them. (On that front, imagine the nerves of Pies fans as Cloke and Tarrant, notoriously wayward left-footers in front of goal, operate together in the same forward line!)

By installing Tarrant as Brown’s full-time replacement, the Pies would be forced to sacrifice some flexibility - which has always an asset, but never more so than now with the introduction of the substitution rule.

The Pies still have Leigh Brown, however, who has been reinvented with remarkable success as a back-up ruckman and key forward who can play competently in any position.

There are also other options to consider.

The Pies might choose to maintain the status quo in their planning for Tarrant as a swingman, thus retaining their flexibility. That, of course, would mean finding another less obvious replacement for Brown, which would require the Pies’ coaching staff to use all of their renowned development skills to fast-track a youngster.

Among the candidates would be two players yet to notch an AFL game: mobile 204-centimetre monster Lachlan Keeffe and 191-centimetre redhead Tom Young.

They are players of contrasting styles, providing different assets and match-up options depending on the opponent and conditions (although the preference would be to give one youngster time to settle into his role rather than chop and change the team and the youngsters’ confidence). Both would be great stories.

Keeffe, who will be 21 in April, was a talented junior soccer player from Gympie, Queensland, and had played just a few under-19s games at amateur level in his native state before joining the Pies as a non-registered rookie at the end of 2008 and making inroads in the VFL.

Young, 19 this April, made his way to Collingwood via the NSW AFL scholarship scheme and won the Pies’ VFL best and fairest last year, averaging 19 disposals a game in defence.

An omen might be their guernsey numbers - Keeffe has No. 23, worn by Craig Kelly, the 1990 premiership key defender and hardman, while Young has been given No. 25, once donned with distinction by that great Collingwood centre half-back and big-occasion player, Billy Picken.

Either way, the Pies can’t lose: on one hand, Tarrant would do a terrific job in defence and on the other, some youngsters would get a taste of AFL football in the competition’s premier team.

And if the Pies take the latter option, they might even unearth the next Ben Reid, who was such a revelation last year. With last year’s premiership side containing six former rookie-list players, no one would put it past Malthouse and his coaching panel to pluck another one from obscurity.

Whatever route the Pies take, they will be praying that Reid and Tarrant remain fit and healthy, which is certainly a concern as both have been injury-prone.

It’s pertinent here to recall Malthouse’s comment last week that if Tarrant and fellow recruit Andrew Krakouer play more than 30 games between them this year, it would be “a real bonus”. (Tarrant played just 13 last year with the Fremantle Dockers.)

Others well be required to fill the Tarrant void.

But, as usual, Malthouse is a step ahead. Regardless of the issues he confronts in relation to availability of personnel in defence, the Collingwood coach already has the perfect antidote: his revolutionary (or should that be evolutionary?) defensive zoning mechanism known as ‘The Box’.

As much as Hawthorn coach Alastair Clarkson compensated for his defenders’ overall lack of one-on-one competence in 2008 by instituting his zone formation, ‘Clarko’s Cluster’ - a precursor to The Box - Malthouse can be confident his side will again concede relatively few inside 50s, and that when they do, often it will be rebounded out of the danger zone by virtue of the ball being delivered haphazardly under enormous pressure.

Of course, another unknown this year is how well opponents will navigate The Box (which, we are reliably informed, has been subtly refined this pre-season). Coaches have closely studied it and implemented strategies to counter it, but if they again melt under intense heat, another Pies flag might well be in the box - er, I mean, the bag.

The views in this article are those of the author and not necessarily those of the club