A 5-2 defense is a defensive scheme in football where there are five defensive linemen on the line of scrimmage, two linebackers, and four defensive backs in the back of the defense. This scheme adds an extra defender on the line of scrimmage, or two depending on the team's usual calls. This format works best against offenses that lean heavily on running the ball.
A 5-2 defense is great for a team trying to stop a run-oriented offense. Having the extra man power in the front of the defensive makes it harder for an offense to successfully run the ball, making the team's offense more one-dimensional.
The one issue with this defensive style is that it makes the passing defense a little bit weaker. There is a give and take with strengthening your run-defense. If you beef up your run defense with a 5-2 scheme, your passing defense is going to get weakened. But, a 5-2 defense is not an every-down defensive scheme. On occasion, one of the five defensive linemen will actually be used as a passing defender.