Former NFL running back Lorenzo Booker shocked college scouts back in 2002 when he bailed on Notre Dame to play for Florida State ... and now TMZ Sports has learned, it was all about chasing tail.

Booker -- who was widely considered the #1 high school running back in the country -- had his pick of college programs back in the day ... and, after making a verbal commitment to play for the Irish, he stunned everyone by announcing he was going to FSU on live TV.

And now Lorenzo tells us why he had the sudden change of heart ... the girls at ND are just flat out ugly and the girls at FSU are a bunch of tan smoke shows. Basically, it was a no-brainer.