Jimmy Johnson’s most famous line is "how bout them Cowboys" but there’s a line he preaches to this day: "fatigue makes cowards of us all." He is entirely correct, as players tire they make more mental errors.
It’s one of the reasons that Chip Kelly preaches high tempo for his offense, and over his two plus seasons as Eagles coach we have seen, sporadically, how an advantage in fitness has given the Eagles an advantage on the field at the end of games. Grinding a team down so they are worn out in the 4th quarter is nothing new, Chip Kelly just tries to take it to an extreme, and it’s a fine strategy.