1) Football player 2) Footballer 3) Linebacker, often 4) Piling-on footballer 
A tackler was a supervisor in a textile factory responsible for the working of a number of power-looms and the weavers who operated them.{r|OED} The title derived from the job, which was to `tackle` any mechanical problems encountered with the looms in their charge. Invariably male, they had a reputation for gullibility and were the butt of many.....
[n] - a football player who tackles the ball carrier
noun a football player who tackles the ball carrier