Just an observation--no dog, no fight--but the straight line across the field measurement would work perfectly from this angle if and only if the field happened to be flat. The slope coming down from the crown of the field tends to make objects closer to the sideline look "lower" from this angle even if they were part of a straight line...note how the straight 18-yard line appears to bend slightly towards the goal as you get to the far sideline end of it. In other words, a player on a straight sideline-to-sideline line with a defender could APPEAR from this angle to be offside if he were standing at a lower elevation due to the slope of the field.
