He was a BEAST at the University of Arizona back in the day -- and now he's going to bat for hoops coach Sean Miller ... telling people to STOP assuming he's guilty of paying recruits!

"I think we have to go by innocent until proven guilty," Shakur says ... "can't assume anything!"

Miller has adamantly denied discussing plans to pay $100,000 to Deandre Ayton -- despite an ESPN report that the conversation was captured on an FBI wiretap.

Shakur not only praises the university for sticking by Miller -- but also says the scandal could actually MOTIVATE the team to kill it in the NCAA tourney.

We'll see ... in the meantime, check out this Shakur highlight.