I think the problem here, is that if the move is provably always fatal, it would not be legit (as this would open up the sports organization running the sanctioned match to all manner of legal issues). So a move that is always fatal would be banned and not legal. Rules generally exist to ensure that the competition is fair, or that the competitors are safe, or to prevent unsafe conditions from occurring. (For example, in NFL Football, you are not allowed to pull on the face guard of another player as doing so could cause the mask to break and could expose the player to all manner of injury or other sanctions. In most Tournament Trading Card games, you are not allowed to touch another players card without first asking for and receiving permission, because taking it from the field without stating intent could result in a physical conflict to occur in a game.). Most rules do have a catch all to allow the scenario not thought of to be short circuited. While there "ain't no rule" that says a golden Retriever can't play Basketball/Football/Volleyball/Organized Calvinball what have you, most high schools in the United States do require that the play of a team sport be a Student of the School they play for and maintain a GPA, qualifications that a Golden Retriever would almost always fail to meet). A simple line about no moves which will reasonably cause lasting injury to the player would give the ref enough wiggle room to rule that a move that will knowingly kill a player would be illegal under this as death is a very well known lasting injury.
That said, whether the ref uses a seeing eye dog or not, the call will likely not affect this as the scenario is definitely pre-meditated murder (1st Degree murder) and the evidence shows that you clearly wanted to kill someone. The judge doesn't care if the tournament didn't declare it illegal, he'll leave the outcome to that decision the the civil court when the players association, and the decease's family sue them for the unsafe environment (and there are probably some regulatatory agencies that would like a word).
Now, if the move was illegal, but the death was unintentional, it could be manslaughter if you actively sought to break the rules, knowing full well this would happen. Many rules are written without the justification of the specific rule. And this is actually a lot harder to prove, because we would need evidence that you planned to violate the rules (you could not intend to violate the rules... refs can call a foul on you for an accident because a game rule is not a law, and failing to follow it could result in a dangerous situation whether or not you intended to follow the rules) any crime of intent is hard to prove because you have to look for clues to actions that are premeditated in nature or require an action on your part (such as deflating footballs). Because you created an unsafe condition by breaking a rule, the death from that injury may be Manslaughter if it can be proven that was intentional rule break, but your goal was not specifically to cause a death of another player. If you break a rule, but had no intent to break the rule and another player dies, it could be an accident and you might not be liable. This situation hinges on your intent to break a rule, which is hard to prove as the game does not care about your intent. Intentional or otherwise, you will be issued a sanction to deter future actions from repeating.
In the United States, there is a legal tradition of "Felony Murder" which is the legal intention for the crime of someone unintentiolly dying while the defendant was committing a non-homicide based crime (I.E. you walk into a bank, pull a gun, fire it into the air, and yell "Down on the Floor, this is a stick up." If during the stick up a little old lady who was patroning the bank has a heart attack, you will be charged with her murder even if you never shot your gun at a person. The fact that your criminal action caused her to have a fatal heart attack is legally a foreseeable outcome of breaking the law, thus you can be held on a First Degree. Similarly, there is Felony Manslaughter, which is the equivalent used for any case where the highest crime committed is a misdemenor offense (I.e. You're driving in excess of the speed limit sign and plow into a car, killing the drive. Since speeding is the only crime committed, the the charge for the death is Felony Manslaughter.).