Clark's son, Jordan -- alongside 2 Arizona State football teammates -- claim they were called the n-word by a Whataburger customer this week ... and instead of de-escalating, the restaurant manager threatened to call the police on the players.

You can read Jordan's entire narrative on the incident below.

Clark spoke on the incident with ESPN's "Get Up" on Friday morning ... saying he's thankful his son is still alive.

"I'm playing out a scenario of if this woman would've had a weapon and she could easily say that these 3 young black men were threatening her ... I believe that if that woman pulls a gun on those young men and that woman pulls the trigger, I believe that she's never punished," Clark says.

"I believe that justice is never served. And, even if justice is served, it's not enough to bring my son back."

"This isn't just a fear for me every day, this has been a fear for black people forever."

"If something would have happened to him, it would have broke me," Clark says. "So for me, I have to do a better job of educating him, and I have to protect him."

"I know it's getting better, but it's not better yet, better for everybody."

Clark says he wishes he would have taught his son to never approach a white person's vehicle ... knowing what could happen if he runs into the wrong person.

The entire segment is powerful ... Clark sobs as he thinks about what could have happened, given today's climate.

As for Whataburger, the chain released a statement on the incident ... saying, "We do not tolerate racism and were horrified to hear how these customers were treated by another customer."