This article uses too much jargon, which needs explaining or simplifying. (September 2012)
A defensive tackle is a position in American and Canadian football.
Defensive tackles typically line up in the center of the defensive line. As some of the largest players (in size) on the field, defensive tackles try to make it hard for the quarterback to throw the ball by blocking offensive linemen and tackles who protect the quarterback. They rarely do anything else.
In the National Football League, defensive tackles may wear numbers in the 50s, 60s, 70s, and 90s, but may wear any number they chose in college football.