IIRC - Nnamdi is strictly LCB and m2m - Philly put him in a zone... like entering a sprinter in a pole vault competition.
Not exactly Dbuc. A great corner should be able to play zone and man coverage. They should be able to get physical at the line, bump and run, and play the ball when it's in the air. A great CB should be good at all these things. It's all part of his job.
A great sprinter doesn't need to know anything about pole vaulting. It has nothing to do with his job.
Also, I won't pretend to know what the hell happened in Philly, but it wasn't just that they asked him to play zone. He was getting lit up in man coverage and missing tackles left & right. He was suddenly bad at everything whether he was in zone or man.