THE AFL has closed a possible loophole in its new bidding system that will stop clubs from being able to trade out early picks and start matching bids for top-rated players with late draft selections.

Under the system presented to clubs in May, there was no maximum deficit and no rule blocking clubs from trading out early picks and then beginning to match a bid with a late pick.

It would have allowed the Brisbane Lions, for example, to trade away their second and third-round drafts picks this year and then use a fourth-round pick to start matching early bids on academy pair Ben Keays and Eric Hipwood.

Both of the Lions' zone prospects are likely to attract first-round bids from rivals. 

However the introduction of the ability to trade future draft picks has seen the AFL look more closely at its points-based bidding system for father-son and academy players and iron out some anomalies. 

It has led to the AFL setting a points deficit limit for clubs bidding on father-son and academy players.

The limit will be set at 1723 points, which is the equivalent of the group of picks that will be assigned to the premiership team each year: selections No.18, 36, 54 and 72.

If a team trades future draft picks in or out, their deficit limit will be altered according to how many selections they hold.

For instance, if a team acquires an extra first-round pick for the following year they have a deficit limit of 2708 points (the standard 1723 plus 985 points, the value for pick No.18).

Conversely if a club trades out its future second-round pick, it will have a deficit limit of 1221 points (1723 minus 502 points, the value for pick No.36).

The move guarantees academy clubs will pay back their deficit in one year and cannot access future picks two years down the line compared to every other club's access to just one draft into the future.  

It also ensures clubs will not be allowed to take their points debt into the following year's draft on a consistent basis, which could have seen them be in a never-ending cycle of owing points for highly-rated players.

AFL.com.au reported last week about the other major change to the bidding system, which saw the AFL decide that clubs matching late bids for academy or father-son picks would not risk pushing back their first selection the next year if they owed points.  

Instead, they will be able to pay back the remaining points in the same round that the bid came.

The AFL confirmed this week the 2015 NAB AFL Draft will be staged in Adelaide on November 24, and it is confident the app it is building with Champion Data to simplify the bidding system will be ready for draft night.

It is exploring ways to further liven up the night, with the possibility of a new format for the calling of each selection.