This drama is top notch! I don't see why it's underrated because it really is a good series.
Fighting for what's right, that is the message you will get from watching this.
I do have some complaints though for example, Kim Do Yeon.

Don't get me wrong, I like him and I was really moved by him in Move To Heaven but he was playing an adult. In Strong Underdog he plays a high school student and I don't think it fits him well because he looks older. I have to say that he did a good job but I just don't think he should play such young roles, he should play an adult as he IS an adult.
I also don't like how the ending didn't show us Min Ah kicking ass. I mean, come on! She was already kinda cool (in my eyes) and then it's revealed that she is a total badass!

Anyway as I said, Strong Underdog is really good and I hope you give it a chance and watch it.