Sorry, Baker Mayfield ... Rashad Jennings says there's NO DEBATE who the rookie of they year is ... and the ex-NFL star says it's "hands down" Saquon Barkley.
TMZ Sports spoke with Jennings about the tight race for ROY between guys like Mayfield, Barkley, Phillip Lindsay and Nick Chubb ... but R.J. says it ain't even close.
It really could go any way ... after each rookie has posted huge numbers this season:
Barkley -- 1,307 rushing yards, 721 receiving yards and 15 TD.