Being a linebacker in football seems like quite the hard work.
Yea linebackers in american football seems very intensive
Definitely! I really don't know what the different roles do in american football.
The linebacker is a defensive player that stays behind the line of scrimmage
That makes a lot of sense, since they are behind a line hence the name.
Linebacker
A linebacker (LB or backer) is a playing position in American football and Canadian football. Linebackers are members of the defensive team, and line up approximately three to five yards (4 m) behind the line of scrimmage, behind the defensive linemen, and therefore "back up the line". Linebackers generally align themselves before the ball is snapped by standing upright in a "two-point stance" (as opposed to the defensive linemen, who put one or two hands on the ground for a "
3–4 defense were Hardy, fellow Butkus Award winner Dana Howard, future NFL player John Holecek, and Simeon Rice. Because of this, Hardy was often overlooked as a linebacker. At his position, he was not prolific in accumulating tackles like Howard, or in quarterback sacks as was Rice, who as a "rush linebacker" played on the line of scrimmage like a defensive end. 
Hardy was recognized as being among the very best linebackers in college football as a senior, winning the Dick Butkus Award and receiving consensus