THE AFL will trial a 15-second shot clock at the remaining NAB Challenge matches at Etihad Stadium, with a player's set-shot time counting down on the venue's scoreboard.  

In a move that could put tardy forwards on notice, a countdown clock will appear when the controlling umpire gives the player his 15-second warning.

It will disappear when the player starts his approach, with the umpire calling time on as normal once it reaches zero.

Players will still have a total of 30 seconds to take their set shot before play on is called.      

The shot clock is one of a number of initiatives being tested at Etihad Stadium before the start of the season, which will improve "interaction and understanding of the game" for supporters. 

Football managers were made aware of the trials last week, with the League confirming the details in a memo to clubs on Tuesday afternoon. 

The AFL limited the time available to players taking a set shot in 2006, setting the 30-second limit as part of changes designed to make the game more fluent.

As well as the countdown clock, fans at Etihad Stadium for this week's matches will hear umpire explanations of free kicks and score reviews.

The free kick explanations will be broadcast during scoreboard replays, while the umpire's verdict during score reviews will be broadcast on the ground's PA.  

St Kilda and Hawthorn kick off the final round of NAB Challenge matches on Thursday night at Etihad Stadium before Melbourne and Essendon square off at the venue one night later.

There is a double-header at the stadium on Saturday, with Richmond taking on North Melbourne during the day and Collingwood facing the Western Bulldogs in the evening.

Meanwhile, the Etihad Stadium roof will be specially positioned this weekend as part of a trial to reduce glare on the playing surface while still allowing the match to take place in open air.

The western roof panel will be moved into a different position so the field will stay in shade during play as the sun moves.

This will happen at Saturday's Richmond-North Melbourne NAB Challenge match and Sunday's Carlton-Geelong clash, as part of a range of initiatives trialled ahead of the premiership season.

A fan survey last year saw 60 per cent of supporters wanted the roof open when the weather was fine.

But the glare on the surface has been a contentious issue for players with some struggling to pick up the ball when sun and shade alternates.

Broadcasters have also said the quality of their product is affected when play deviates between the light and shade.

The League's roof policy will remain the same this year, which means it will be open for afternoon games if the weather forecast permits.

When there is more than 30 per cent of a chance of rain, it will be closed before the venue is open to the public.

It will also be closed for night games.

Opening and closing the roof while patrons are inside is against the stadium's safety policy, and that is not expected to change this year. 

At the end of the NAB Challenge clubs, players and fans will be consulted for feedback on the trials, which won't be rolled out at other venues this pre-season.