ASU Fan Brawl -- I WAS PROTECTING PREGNANT DAUGHTER ... Says Old Man

The old man who booted an ASU student in the face during a recent football game has finally broken his silence ... telling TMZ Sports he only got violent to protect his pregnant daughter from a pack of aggressive, drunken jerks.

The man who fired the kick, who wants to be identified as "Mark," says the group of students started picking on him because he accidentally wore a blue shirt to the ASU vs. U of A game (blue is one of UA's colors).

Mark -- who insists he's a diehard ASU fan -- says the students not only harassed him verbally, but started closing in on him and his family, which included a pregnant daughter ... and he got scared.

That's when one student finally got too close to Mark's comfort "bubble" ... and he took matters into his own feet.

After the kick, the students piled on Mark, but he says he was barely touched. Mark claims his daughter was hit in the stomach, but she's ok.

Mark says he's not proud of the incident, but believes he did what he had to do to get out of a tough situation.

As for the students, we're told they're saying Mark was the one who had been running his mouth prior to the altercation ... and he's the real bad guy since he threw the first blow.