With the impeccable modern NFL track record of Ohio State QBs this should be a slam dunk.
Hey now, former Buckeye QB/P Tom Tupa had a long career (@17 seasons) in the NFL. Okay, he was primarily a punter in the NFL but he still found enough PT at QB to pass for 12 TDs. And Mike Tomczak was on an NFL roster for 15 seasons -- not bad for an undrafted player coming out of college. He even got a Super Bowl ring with the Bears as a rookie.
In the end, I think Fields will have a decent NFL career. He's a smart, grounded and ultra-athletic kid.