All the attention might have been focussed on the AFL's national draft in Queensland last week, but in the off-season an equally intriguing swap meet has been going on in football.

That is the growing trade in assistant coaches, those men who on the surface do little more than occupy seats in the corners of coaches boxes, hold up magnetic boards and move witches hats at training, but who have become some of the most valuable commodities in the game.

As many as 20 assistants changed teams since the end of the season, as clubs try to get an edge by poaching the intellectual property of their rivals. Unsurprisingly, it is the successful clubs - Collingwood, Geelong and St Kilda - who've had their staff targetted, and lured away with tempting offers. They've each lost two members from their 2010 panel.

Witness the ruthlessness which Essendon pursued, and caught, Cats' senior coach Mark Thompson and his highly regarded offsider, Brendan McCartney, even though the latter was just one year into a four-year deal.

Leigh Tudor is another classic example, having been poached from two leading clubs in recent seasons, presumably because of the IP he brought along with him. He was recently tempted away from St Kilda to Sydney, having been poached by the Saints from Geelong a couple of years earlier.

So the trend has become clear: the higher your club moves up the ladder, the more likely they are to lose coaching staff at the end of the year.

Saints coach Ross Lyon highlighted the growing phenomenon when he spoke with sports radio station SEN this morning.

"There is no doubt that it happens. I think we're naive to think that it doesn't happen, and it seems to happen to the teams at the top of tree," Lyon said.

"I think if you look at the clubs that they are targeting they have all been successful.

"I have no problem with it, it's just supply and demand and we sought after some of Geelong's intellectual property when we targeted Leigh Tudor."

Because the Cats have played in three of the last four grand finals, their coaching panel has been in especially big demand. "Clearly Geelong's football people are really valued, Brendan McCartney has a huge reputation. I think they (Geelong' assistant coaches) have been sought after," Lyon said.

When a team was attempting to rebuild or challenge for a top-four position, Lyon suggested that it was easier to target an assistant coach who has been involved in a successful environment instead of developing one from scratch.

"Why wouldn't you go after the Thompsons, McCartneys, the Leigh Tudors, and those types when you know they can bring you up to speed quickly?'' he said. ''There are some clubs who've had a gap in their game plans compared to the best. There is no doubt about that."

After Collingwood won its 15th premiership this year, its assistants were being targeted before Mick Malthouse had time to put the cup in the trophy cabinet. And it was his rival coach in the two grand finals who was partly responsible for causing that unrest.

"Collingwood have lost a couple, Gavin Brown has gone to Carlton and Paul Hudson has come to us," said Lyon.

The introduction of two new teams into the competition in the next two seasons will put further pressure on the system, as assistant coaches with a good pedigree get targetted.

"If you are in strong systems, people will pay to get your IP, there is no doubt about that, and the new franchises have got an enormous amount of money,'' Lyon said.

"It is a wonderful opportunity for coaches, and young coaches to grow, and list managers and senior assistants.''

In the past six weeks there has been at least 20 assistant coaches who have changed clubs - the majority of which have gone from top eight teams.

THE MOVERS AND SHAKERS

Paul Hudson - Collingwood to St Kilda

Gavin Brown - Collingwood to Carlton

Leigh Tudor - St Kilda to Sydney

Andy Lovell - St Kilda to Gold Coast

Brendan McCartney - Geelong to Essendon

Mark Thompson - Geelong to Essendon

Leon Cameron - Bulldogs to Hawthorn

Chris Scott - Fremantle to Geelong

John Barker - Hawthorn to Carlton

Matthew Lappin - Carlton to Collingwood

Brett Montgomery - Carlton to the Western Bulldogs

Robert Harvey - Carlton to St Kilda

Peter Berbakov - Sydney to St Kilda

Adam Kingsley - Port Adelaide to St Kilda

Todd Viney (pictured, above) - Adelaide to Melbourne

Sean Wellman - Melbourne to Essendon

Alan Richardson - Essendon to Carlton

Gary O'Donnell - Essendon to Brisbane

Craig McRae - Richmond to Collingwood

David Teague - Carton to West Coast