Powell explained his decision to transfer to TMZ Sports ... saying he believes the vaccine should not be mandatory because "people are getting the shot and still getting sick." Powell tells us he contracted COVID before last season -- and said he had "a headache for a few days but I'm fine and…

The University of Tennessee says they found no evidence that Greg Schiano helped cover up child rape during his time at Penn State ... but they're still not explaining why they backed out of hiring him as the Vols head football coach. FYI, Schiano was reportedly signed to be the next head coach --…