Although college football coaches have different recruiting requirements, when selecting defensive backs, they all commonly look for a few key attributes.
To be a DB in college, you've got to have speed for coverage. Coaches want athletes who can keep up with or outrun fast wide receivers. Most of the time, DBs do not run straight ahead, so their speed is measured through backpedals, shuffles and quick breaks on routes. (Check out some great football-specific drills to build up this trait.)
Some athletes take awhile to get moving, while others get up to full speed in a hurry. An explosive first step is vital for a defensive back. You must be able to move in and pick off cuts as fast as possible. Explosiveness in a DB is the difference between an interception and a tackle for a five yard gain. (The keys to explosiveness.)
Many claim the DB is the most athletic position on the field; and as a former D player and coach myself, I have to agree. You must perform the unnatural motion of backpedaling, not knowing where your opponent will go. A lot goes into evaluating the athleticism of DB prospects. Although speed, proper footwork and explosiveness are crucial elements, you also need:
DBs need to be intelligent on the field. When they play smart, it's special. Coaches want to feel confident that their DBs understand all the coverage checks and adjustments that need to be made before the snap, and that they are able to make split-second changes while running at full speed.
Coaches love physical DBs. In high school, DBs are not expected to play a huge role defending the running game, but that changes dramatically in college. DBs are important in most defensive schemes, being gap sound and stopping the run. A high school DB who plays physical gives himself a huge advantage in recruiting.
Feel free to contact me directly with any specific DB questions you may have @PWCurran.