Goombah makes some excellent points. Whereas many college receivers make it easy for their qbs by running away from defenders, in the NFL everyone in the secondary can run. Also the coverages and blitz schemes are far more complex in the NFL than in the best college programs.

One measure that's been helpful in determining what college qbs will find success in the pros is the rule of 26-27-60. A qb, who scores at least a 26 on the Wonderlic, has startes 27 college games as qb, and completed 60% of his passes has a high probability of being a successful pro qb.