The bump and run is a defensive technique used by defensive backs when covering a pass. In a bump and run, the defender will seek contact with one possible pass receiver right after the snap, using his hands to bump the opponent's chest, shoulders, and arms, slowing him down, and making it difficult for him to advance and to position himself properly to receive a pass from the quarterback.
By doing the bump and run, the defender can distort the receiver's passing rout, and disrupt the quarterback's pass timing with him, all of which can lead to incomplete passes and interceptions in some cases. Also, by slowing the timing, the defender gives his defensive line more time to pressure the quarterback, which leads to more sacks. This technique is used by defensive backs of any level and age.
For a defensive back to execute a bump and run well, it is not crucial for him to be extraordinarily fast or athletic, but rather to understand the technique and know the receiver's routes. A good bump and run starts with a good stance, where the defensive back's feet are parallel, the knees bent, and the hands ready to seek contact. The stance allows for quick lateral and back movement. After that, it is important for the defensive back to bump and not lose balance; that way if the receiver gets free, it will be hard to recover.