When the going gets tough, the tough gets going, this is the moto of the Tough guy. They are the people who protects the group and will fight for their ideals. They tend to be rough around the edges but will do anything for their team. But not all tough guys are built the same and just like a leader they have different flavors.
A tough guy can take damage that no one else could survive, like wolverine, or be the battle mastermind. Or like Toph in avatar, someone who does not back down in the face of battle. The tough guy is an important team member because, frankly, a fight can always happen, and sometimes, the group needs to be forceful in their approach, and having the leader just running in and punching people tends to be looked down.