The headbutt feels like a slap on the wrist, particularly when poor technique in tackles and cleanouts are routinely penalised strictly.
It was because it didn't connect.
I think the explanation for it was pretty reasonable.
“The FPRC deemed the act of foul play merited a low-end entry point of 6 weeks primarily given that the Player and victim player were “head to head” prior to the incident, and that the Player’s head appears to have made limited contact with the head of the victim player and rather made contact with the chest area of the victim player. There was also no injury to the victim player.”
“The Foul Play Review Committed emphasised that had there been more forceful head contact made, the entry point may well have been higher than low-end.”
“The entry point for the offence is 6 weeks.”
“The Foul Play Review Committee applied a discount of 3 weeks for entering an early guilty plea (and other relevant mitigating factors including the Player’s otherwise unblemished disciplinary record), reducing the suspension from 6 weeks to 3 weeks.
Further, where a matter is determined to be low-end offending, there are off-field mitigating factors, and the sanction would be wholly disproportionate to the level and type of offending involved, a sanction below 50% of the sanction may apply. To that end, the Foul Play Review Committee considered a sanction of 3 weeks would have been wholly disproportionate to the level and type of offending involved, and applied a further reduction of 1 week to the sanction, resulting in a total sanction of 2 weeks.”