No.
You are not considered a "legal weapon". Your pro or amateur training is supposed to give you more self control, not less.
Yes.
You can get into tons of trouble in a street fight whether you are trained or not.
1.The other guy might sue you for assault, and win in court, even if you did not start it. It is just his word against yours (sometimes even if you have credible, independant withnesses) because you never know how it will go in court. Is jail time worth the risk? Only you can answer tthat for yourself.
2.You or the other person might get seriously injured. There is no referee on the street to ensure personal safety, and no one to stop the other guy (and sometimes his five friends you never noticed) from stomping on you head for five minutes after you have been knocked out cold by that bottle from behind. Or, maybe you "win" but the other guy cracks his head open as he falls on the concrete. Are we prepared to live with that?
Even for legitimate self defence, we need to be aware of the law and also consider personal safety if we do use boxing or martial arts as a response to univited aggression. (self defence). A number of posters have made some good points about that already.
You can defend yourself, but the law will not tolerate an excessive response to aggression. And even if you know this and are very careful, there is still no guarantee that a judge will believe your story if it goes to court, and no guarantee that your training will be effective in saving you injury to yourself or the other party.
I am a boxer, but I think the best training for self defence is a course in self defence. You learn to avoid trouble in the first place. Street fighting is for idiots.(Too much risk, and no prize if you "win".)
I also think Judo and wrestling is probably the best reponse if there is no way to run (and there is usually a way to talk your way out of it or exit).
A judoka or wrestler can at least offer a controlled response that can be effective and not cause serious injury or look like a street fight to witnesses.
A striking response always looks like a fight, and can hurt someone (not the objective, surely, to some drunk guy who makes a pass at your girl). A wrestler's arm or wrist lock will convince most drunks to back off, and there is no shattered orbital for the lawsuit.
Peace is the objective on the street, battle sport in the ring.