Over the past few decades, the back three has been a relatively scarce phenomenon—used now and again to modest effect by the occasional Italian side, the Chilean national team, and a few other spotted squads looking to bolster their defensive line.
But in the past 18 months, it’s spread like wildfire. Suddenly, a significant percentage of the best teams in the men’s games are playing with a back three. And while the trend hasn’t taken over the women’s side with quite as much force, it’s certainly on the radar for the US women’s national team, who experimented with a three-back approach last fall and look set to test it out against stiffer opposition in the SheBelieves Cup.