Yeah alot of linemen weigh 300+ but most linebackers are around 250-270. Linebackers are generally the ones who deliver the hardest hits becaue they're significantly faster then linemen and bigger then corner backs but maybe not as speedy.
Most career ending hits come from repeat breaking of bones or concussions because after you have one or two, it gets easier to have three through nine. And yes most injuries in football can be traced back to individual hits, there's plenty of NFL commentaries where retired players will name the game and the specific play which ended their career. Ham string pulls and sprains are sometimes grounds for retirement but more often then not torn ligaments are more often the case.
True your pads can be a weapon but then again the biggest one hit career killer is the spear. When you spear some one you risk becoming parapalegic which not only ends your career but also turns your life into a whole nother direction. There are also collisions and little man vs big man incidents where the people doing the hitting sustain concussions just as well. From ANY angle you look at it you run the risk of getting injured, hitting or delivering the hit. 3 1/2 year career means people get put out for numerous reasons, and is why any sports and health trainer will tell you why NFL really stands for Not For Long.
