the rule is vague as to the spot........it says the ball is dead but it doesn't mention where to mark the spot
RULE 7 Ball in Play, Dead Ball, Scrimmage
Section 2 Dead Ball
Article 1: Dead Ball Declared.
An official shall declare the ball dead and the down ended:
(d) when a runner declares himself down by sliding feet first on the ground. The ball is dead the instant
the runner touches the ground with anything other than his hands or his feet; or
Note: Defenders are required to treat a sliding runner as they would a runner who is down by contact.
Point of emphasis
Quarterback Slide
Once a runner begins a feet-first slide before contact is imminent, defenders cannot make any forcible contact and must treat a sliding runner as they would any runner who is down by contact. Once a runner begins a slide and becomes protected, he can no longer advance the football, regardless of contact by an opponent. Runners who slide sideways or headfirst will not have special protection.
Runners (especially quarterbacks) who want the protection afforded sliding players must make every effort to slide feet-first before contact is imminent. If a runner starts his slide when contact is imminent, a defender is not prohibited from making forcible contact, as long as it is below the head/neck area.