What to make of the replacement of the other halfback from the top illustration by the fullback in the bottom one? Well, if the wingback were playing in a true wingback position but named halfback, then the other "halfback" would be playing deeper and thus deserve the name fullback. Another justification is that the player positioned as the left halfback in the top illustration tends to have the fullback characteristics described above. But rather than call the faster, lighter back behind (and in this formation, to the left of) him a halfback and so contradict the distance-back-determines-the-name principle (and rather than add rugby's three-quarters back), we call that player "tailback"—the tail of the formation, farther back than the fullback. Even when two players positioned to take a thrown snap in a single wing formation are level with each other (i.e. at equal depth), the faster one (usually playing weak side) is often called the tailback and the more massive one the fullback.