The NRL is considering tightening its concussion protocols following a spate of incidents in the opening rounds of the season. One being investigated involved Parramatta hooker Nathan Peats, who vehemently defended coach Brad Arthur against suggestions he overruled the club doctor.

"I'm not going to get into it too much but the one thing that pissed me off is when people were saying Brad threw me back on or overruled it," Peats said.

"He's our coach and he's also our mate too. He would never, ever jeopardise my health. He's just coaching and he gets the all-clear to put me back on. That's the only thing that annoyed me a little bit."

The governing body is looking to investigate any loopholes the clubs are using to either bypass the concussion protocols or to buy an advantage, such as a free interchange by feigning a head knock. A respected sporting medico, on the condition of anonymity, claimed another rort was players underperforming on CogSport tests in pre-season to ensure that, when they are re-tested post-concussion following a game, they are more likely to be cleared to return for the next fixture. The practice, known as "sandbagging", requires the subjects to register lower initial scores without being caught out doing so.

"It's a genuine issue," the medico said. "It's something the NRL needs to look into."

Professor Kristi Erdal, of the University of Colorado, is one of the world's foremost experts on 'sandbagging' and has written a paper on the issue. She believes independent experts, rather those employed by sporting clubs, should undertake testing to ensure there are no conflicts of interest.

"'Being tested by their own clubs' is the problem," Erdal told Fairfax Media.

"Most professional sports in the US have an independent tester – the conflict of interest and money involved is known to be too much to avoid temptation. Most collegiate sports in the US, however, do baseline testing within the university ... Even under the best conditions (i.e., independent tester, computerised test), my research shows that about 11 per cent of athletes were able to sandbag the baseline test without detection (the ImPACT test, for instance, has validity scales in it to detect sandbagging)."

Erdal said sandbagging was undoubtedly an issue in professional sport but it was hard to quantify how widespread it was.

"It is an issue, it's just a matter of how much of an issue," she said.

"That is, many professional and collegiate athletes have talked about sandbagging baselines openly or wanting to or thinking about it. So one can imagine that if some talk about it openly, many, many more likely talk about it (or have done it) privately. But these numbers are very difficult, if not impossible, to determine without confessions."

The NFL is tweaking its own concussion policies and there was an agreement during the week to adopt a system in which independent spotters have the authority to stop games for a medical timeout. The system would allow the medico to directly communicate with field officials to call a halt to proceedings so that a player can be evaluated. The measures are being dubbed the 'Edelman Rule' following an incident from Super Bowl XLIX, in which Patriots wide receiver Julian Edelman was rocked in a helmet-to-helmet collision. Although he appeared dazed, Edelman remained on the field and caught the decisive touchdown pass from Tom Brady.

The NRL is still investigating the Peats incident, as well as other possible head knocks including one to South Sydney star Adam Reynolds in round two.