Here's why:

* Tension is the force that exists within a rope, cable, or similar object when it is pulled taut.

* In tug-of-war, the teams are pulling on the rope, creating tension within the rope itself.

* The tension force acts in opposite directions, pulling each team towards the other.

* The team that exerts a greater tension force on the rope will eventually pull the other team across the designated line.

While other forces are also present, such as friction between the players' feet and the ground, and gravity acting on the players and the rope, tension is the main force that drives the action in a tug-of-war.