A cornerback (CB) (also referred to as a corner) is a member of the defensive backfield or secondary in American and Canadian football. Cornerbacks cover receivers, to defend against pass offenses and make tackles. Other members of the defensive backfield include the safeties and occasionally linebackers. The cornerback position requires speed and agility. A cornerback's skillset typically requires proficiency in anticipating the quarterback, back-pedalling, executing single and zone coverage, disrupting pass routes, block shedding, and tackling. Cornerbacks are among the fastest players on the field.