0_Apprentice
What exactly is a linebacker? Thats an american football position right
1_Wizard
Yes, a linebacker is a playing position. American and Canadian football use this term. 
0_Apprentice
what exactly is thir job on the team and in game?
1_Wizard
Well, a linebacker is part of the defensive. They will line up about 3 to 5 yards behind the line of scrimmage, which is behind the defensive linemen. That's how they 'back up the line'. 
0_Apprentice
ahh ok, that makes a lot of sense, anything else you can tell me?