Ex-NFL Star Mike Williams -- Coaching Middle School ... Wants to Be USC's 1st Black Head Coach

He killed it at USC ... and spent several seasons in the NFL ... but now ex-wide receiver Mike Williams has a new goal -- to be USC's first black head coach ... and he's starting by coaching at an L.A. middle school.

The 31-year-old tells TMZ Sports he officially hung up his cleats -- but says he's always had a passion to coach. So when he moved back to L.A., he started hunting for jobs to get his new career off the ground.

"I applied for a couple of high school jobs ... schools that I thought would have good athletes ... but some of those schools didn't even call me back for an interview," Williams says.

But one place that did have interest was the prestigious Brentwood School in L.A. -- where tuition runs $35k ... and boasts famous alumni like Fred Savage and Adam Levine.

"Brentwood really presented a great situation for me. I was able to assist with the varsity team, and then head the middle school team."

Williams says he's having a blast so far -- and is excited to share the wealth of football knowledge he's picked up over the years ... especially what he learned from Pete Carroll, who coached him in college and in the pros.

"What I learned from Coach Carroll is he allows guys to be exactly who they are ... as long as it's in the confines of what the team is trying to do. That's why you see all these personalities coexist ... and in a winning fashion. Be who you are as long as you ballin."