THE AFL's much-discussed 'third man up' rule is set to be debated again after Richmond midfielder Shaun Grigg successfully introduced a potential new tactic.  

Grigg sneakily won a free kick and slotted a crucial goal with the tactic midway through the fourth quarter of Thursday night's 19-point win over Collingwood.  

The AFL banned the 'third man up' in ruck contests in the off-season after it became a popular approach among clubs last year to curb dominant big men.  

One player at each club must nominate before every ruck contest and the rule already caused some confusion in round one.  

The umpire paid a free kick against Grigg's bemused Magpie opponent Brayden Maynard for "blocking" and explained the Tiger had nominated himself for the ruck.  

Collingwood big man Jesse White was in the vicinity and expecting to contest the boundary throw-in.

Tigers coach Damien Hardwick had no doubt Grigg was seeking a free kick.  

Grigg, who is 190cm, kicked a 50m goal courtesy of the free kick, extending Richmond's lead to 20 points at a key stage with the Pies pressing.  

"Collingwood has to be onto that. Grigg's taken the last three boundary throw-ins," Richmond great Matthew Richardson said in Channel Seven commentary.  

Magpies skipper Scott Pendlebury told 3AW post-match he was concerned about the Tiger tactic.  

"I don't think we want to get the game looking like that," Pendlebury said.  

"All sides will see that tonight and think they can take advantage of that. Every side will think, 'Gee, we might be able to steal one if we can do this'. It might happen."  

Collingwood coach Nathan Buckley said the Grigg goal was "costly" and Maynard would have learned a harsh lesson about being aware.  

"Brayden is a young player (and) he's still learning. At the very least he should be watching the ball," Buckley said.  

"You shouldn't have your back to the ball and maybe that would have been enough."