I'm certainly no expert on football; my football experience happened 50 years ago, on the school playing fields, where the main objective was to stay out of the way of the ball as much as possible while freezing to death in inadequte clothing. Cricket was much better; it was in summer (football was winter), it was easy to stay out of the way of the ball, and you didn't freeze.
But I'm quite sure that, although no-one told us of a rule against biting players arms, there was an implicit rule that forbade it. I mean to say; it shouldn't be necessary to tell people not to bite other people.
I'm not shocked that some footballer has done this. And, from what I hear, it isn't the first time for him. What shocks me is that the debate is about whether he should be banned from three games or seven.
If I were playing against him, I'd refuse to go on the field unless he were properly muzzled. I wouldn't ask him to be totally banned from playing; that's his profession, after all, and if he weren't allowed to play football for money, he'd have to get a proper job as a chef or a programmer. No - it's clear to me that the chap needs to wear a muzzle, just like a dog that has bitten people before. That way, he can continue to play the beautiful game, and yet opposing players will feel protected against his teeth.
And maybe they should also make sure that his fingernails are properly trimmed.