The same idea as 3rd Down Splits, isolated to 4th down plays -- the highest-leverage down in football.

Inputs: Every play on file where down = 4 and this player was involved.

How a player performed once his team's offense (or the opponent's, for a defender) reached inside the 20-yard line.

Inputs: Every play on file within 20 yards of the goal line (`distance_to_goal <= 20`) this player was involved in. COVERAGE CAVEAT: true field position is only recorded for about a third of plays leaguewide, concentrated in FBS/FCS games -- a player whose games come from a source without it will show thin or missing red-zone splits even if he played plenty of red-zone snaps. This is a gap in the underlying play-by-play data, not a sign he didn't play there.

A 7-tier rule (bigger lead required as the clock runs down) that flags plays happening in a game that is no longer competitive -- e.g. a 30+ point lead right after halftime, or a 12+ point lead inside the final 3 minutes.

Inputs: Quarter, game clock, and the score of both teams at the time of the play. Garbage-time plays are not thrown out -- they count for 35% of a normal play in every "garbage-time-adjusted" figure, so a player who pads stats once a game is decided shows up as such rather than being invisible.