It's a n00b question because it can't be answered with any accuracy. A few owners have 100 seasons under their belt. So, at max, they've drafted less than 3000 players. Of those 3000, I'd be surprised if more than 50 have fallen under the "probably won't sign" category. Of those 50, they probably haven't even bothered to offer half of them a contract. At the end of the day, even the most experienced owner has going to have dealings with 25 of these players. Therefore, if he signed 5, is the answer 20%?
OR IS IT A RIDICULOUSLY SMALL SIZE WHERE ANSWERS CAN ONLY BE BASED ON HEARSAY AND BEST GUESSES?!?!?!?!?!?!?
If so, the exact number is 23.74%.