Grounding the ball ... last year's awarding of Billy Slater's try against Manly would not be a try this year.

Grounding the ball ... last year's awarding of Billy Slater's try against Manly would not be a try this year.

REFEREE boss Daniel Anderson has appointed former players Luke Patten, Matt Rodwell and Justin Morgan as video referees for 2013.

Anderson, who also intends to have two officials in the video referees' box for all matches, announced the trio as part of a push from the former NRL coach to increase the number of former players among the refereeing ranks.

The trio will take part in a level-one referees course before the start of the season, with Patten to make his debut alongside Steve Clark in the Charity Shield match on Friday, February 22.

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Shoulder charge ... the defender doesn’t have to wrap his arms around the ball carrier but must at least attempt to.

''They will be part of a two-man team to ensure no errors occur upstairs,'' Anderson said.

The obstruction rule, which was the subject of great debate in an error-plagued season last year, was again discussed at Wednesday's briefing.

Anderson admitted there would still be some grey area around the rule this year but believed he had minimised the uncertainty with new interpretations.

No try ... unless video evidence suggests otherwise.

No try ... unless video evidence suggests otherwise.

He had instructed referees to penalise a blocker if he made any contact with the defensive line, encouraging players to stop before the line or run through it without impeding a defender.

The message had been relayed to all 16 coaches, who had worked overtime in the off season to ensure players were aware of it.

''You can't run at defenders and initiate contact and the defensive line cannot be disadvantaged,'' Anderson said.

Try ... the referee's decision can only be overturned if evidence suggests otherwise.

Try ... the referee's decision can only be overturned if evidence suggests otherwise.

Regardless of whether the impeded defender had any chance of making a tackle, the referees would penalise the offender, even if the infringement was made at the ruck and the try was scored out wide.

It's an interpretation that Australian coach Tim Sheens believed could provide more obstacles than answers. Sheens was concerned coaches and players would try to exploit the rule.

But Anderson defended the decision to penalise all contact made by decoy runners, regardless of its impact on the play, and insisted there couldn't be exceptions to the rule based on how far the play had gone after the impact.

Under the new interpretations, the attacking team would not be penalised if the defender initiated the contact on the blocker.

He also gave a detailed explanation of how the video review system would work under the new rules.

If the on-field referees wanted to double check a ruling, they would have to make a ''live decision'' - try or no try - before sending it up to the video referee for review.

The decision could only be overturned if there was sufficient evidence to suggest the on-field referee's live decision was incorrect.

''There was too much going upstairs last year,'' Anderson said. ''Referees have an instinct and are usually in the best position to make a call and we want them to have the confidence to do that.''

There was also some clarification on the banned shoulder charge. A player would escape penalty if he attempted to wrap his arms around the ball-runner.

Explained: The NRL's rule adjustments

LIVE DECISION, TRY: If the referee thinks it's a try but wants to review the play, he will signal after calling time off and initiating the review. His original decision can only be overturned if evidence suggests otherwise.

LIVE DECISION, NO TRY: The onus is on the referee to make a live decision before asking the video referee to review his initial decision. If he thinks it's not a try, he will signal after calling time off and initiating the review. His original decision can only be overturned if evidence suggests otherwise.

GROUNDING THE BALL: Billy Slater's try, pictured, when he grounded the ball with his arm but has lost control. It was called a try last year but would not be a try this year.

BLOCKING: Referees will penalise players who don't attempt to catch the ball but impede the path of the chaser.

OBSTRUCTION: If a defender initiates the contact with the block runner, it is not deemed to be an obstruction.

SHOULDER CHARGE: If a defender makes no attempt to use his arms on the attacking player in the tackle, he will be penalised for a shoulder charge. The defender doesn't have to wrap his arms around the ball carrier but must at least attempt to.

OBSTRUCTION: If the block runner initiates contact with a defender, the attacking team will be penalised, even if the impeded player has no chance of making a tackle. The block runner must stop or run through the line.

OBSTRUCTION: The ball-runner is not permitted to run behind an active block runner, regardless of the depth, if he disadvantages the defender. A try was awarded last year but wouldn't be this year.