What's the problem if you started "the fight" (which should be a carefully arranged beat down of your target, nothing resembling a fight)? Your objective is to stop the bullying, not be perceived as an angel (well, except for possibly those terrible Old Testament smiting types).
The problem is that you get removed from school and given a label of "potentially violent" which will follow you around for a while.
Some countries will prosecute youths involved in violence. Even if prosecution is avoided there might be something like the English "caution" where the person accepts their guilt and accepts a caution (which is kept on record) in order to avoid prosecution. This could also follow you around. Being arrested could make travel to another country tricky.
Finally, beating one or two bullies might not be sufficient. If there is a group of people around you could end up very badly beaten, perhaps hospitalised, and potentially even dead.
Note that I'm not in the USA. That consequence doesn't exist in my country, not if you are provoked.
And note that I agree. Allies and Authorities are a good mean of fighting back.