The CBs or the Safeties can be the Force player in the 4-3 defense depending on your coverage philosophy and personnel. Most teams ran Quarters coverage vs. the Georgia Tech Flexbone in 2009 and utilized their Safeties as the Force players. The CB in Quarters coverage is is a pass-first defender who is man vs. his WR unless he runs a Shallow route or unless he cracks the Force player, the Safety. When the WR crack-blocks the Safety, the CB will then become a run-first defender. If he does not, the defense will have nobody on the pitch back, allowing the Flexbone offense to make big plays on the perimeter.