Math Question No Touchdown for Football Fans

From the Boston Globe, now here's a case of "math in the real world" not working out quite as expected:

On an end-of-grade test this month, seventh-graders had to calculate the average gain for a team on the game's first six plays. But the team did not gain 10 yards on the first four plays and would have lost possession before a fifth and sixth play.

The team opened with a 6-yard loss, a 3-yard gain and a 2-yard loss, which would have made it fourth down with 15 yards to go for a first down. The team's fourth play was just a 7-yard gain, yet it maintained possession for a 12-yard gain and a 4-yard gain on two additional plays.

So do the creators of math problems have an expectation to be grounded in reality or is the football example above just a variation on the old "imagine a spherical cow" or "the frictionless ice" or "the chicken and a half can lay an egg and a half every day and a half" types of fiction for the sake of example that comes with the territory in math and science problems?