Ahhh, there is really no telling whether it is reasonable or not. If there are witnesses, then they will report what they see. If you took a martial stance, and as the guy reaches for you, you drove a straight right fist into his mouth, shattering his teeth and breaking his jaw in two places, you will likely lose in court.
And, if you are trained, and you did get the first strike in, with your hips turning and arm rotation, you will certainly bust something up real bad on his face.
If on the other hand as you say, you throw your arms up in a defensive position and as he reaches for you, you block him off his center, and project him away and run, you hopefully get out of the situation and stay out of court.
Obviously there is a great differene between fighting and self defense. Sometimes, you have to turn it into a real fight, but we should be aware of the issues, and what is going on.
I assure you, if you hurt the person seriously or even a little, you will be in court, and subjectivity and perception will prevail. When they find you are a trained martial artist, well more issues will be considered and you look like the bad Kung Fu guy, right or wrong.