You need a clear determination of the OB line. A blade of grass cannot be that line because it can be easily moved by footsteps or disc contact. A moving OB line is very very bad.
So the OB line instead would be the edge of the pavement, regardless of how individual blades of grass might be hanging over it.
Try that out when the road is not paved.
It makes for a poor O.B. line and would be inexcusable for tournaments, but it's the kind of thing you might encounter in casual play. The road (dirt/gravel) is O.B., the grass is I.B., the exact line is extremely difficult. "Touching the grass" may be the best, though distasteful, answer.