The cost of GLT is unjustified for a relatively rare scenario  In order for a goal to stand, the ball must completely cross the line; to have a situation where this is in doubt is very rare. Introducing GLT would be to completely change the nature of football for the least significant occurrence.  These incidents tend to balance out over the season. Teams do not win leagues or are not relegated because of one isolated incident in one game; they win because of skill, strength and tactics, over the course of 90 minutes for a game, and a whole season for a league.