SNP genotyping is the measurement of genetic variations of single nucleotide polymorphisms (SNPs) between members of a species. It is a form of genotyping, which is the measurement of more general genetic variation.
On most plays, the center will snap the ball directly into the quarterback's hands. In a shotgun formation, the center snaps the ball to the quarterback lined up several yards behind him.
A snap is made by having a player, usually the center or long snapper, crouch over the ball in the manner of an offensive lineman and toss the ball backwards between his legs to whichever player is meant to receive the snap on that particular play.