How is cannabis performance enhancing?
If anything he should be commended if he can toke the green and play rugby league, it's really hard to do it. It does disable the players ability not enhance it.
Poor guy, unfair decision
No one has said it was performance enhancing, just that it is a banned substance. I'd say most recreational drugs aren't performance enhancing, they're still banned substances though and that's because they're illegal and thus their use supposedly brings the game in to disrepute. Note this is not my opinion or in line with what I personally believe, just the reasoning behind why some non-performance enhancing drugs are banned.
Substances have to meet 2 of 3 criteria to get banned. From the United States Anti-Doping Agency:
http://www.usada.org/resources/faqs.aspx (under the "code" section)
Q: How does a substance or method get included on the WADA Prohibited List?
A: A substance or method will be considered for the WADA Prohibited List if the substance or method meets two of the following three criteria (none of the three criteria individually is sufficient to add a substance/method to the Prohibited List). 1. Medical or other scientific evidence, pharmacological effect or experience that the substance/method has the potential to enhance sports performance. 2. Medical or other scientific evidence, pharmacological effect or experience that the use of the substance/method represents an actual or potential health risk to the athlete. 3. WADA’s determination that the use of the substance/method violates the spirit of sport.
In this case it would be argued that Marijuana breaches 2 and 3. Although 3 is incredibly subjective the governing body would argue that breaking the law is against the spirit of sport.
I don't necessarily agree with this (especially in regards to Marijuana) but to fail three drug tests when you know it's a banned substance is stupid. No sympathy here.