A free safety is a defensive back who plays in the secondary. Their objective is to prevent long pass plays and runs plays in the middle of the field.
In most leagues defensive units are used instead of individual defensive players. However in IDP leagues individual defenders are thrown into the mix. That means you can draft defenders and you are able to start them and get points for their actions.
Free safeties can earn points the same way all defenders can, with tackles, sacks, interceptions, fumbles forced, fumbles recovered, blocks, and touchdowns.
When drafting a free safety it is important to first read the scoring rules of your league. Knowing what type of actions get you the most points helps you out big time. If interceptions are not as valued and scored similarly to the chart above (one interception is the equivalent to four tackles), then draft a free safety with a lot of tackles instead of interceptions. The league leaders in interceptions usually end the year with around eight to ten interceptions. However, the league leading tacklers are at about 150 tackles. 150 points compared to 32 is a no brainer, take a good tackler!
Some leagues try to fix this problem and make a balanced scoring league, in which case take a free safety that can do it all! Guys like Harrison Smith, Eric Berry, and Eric Weddle can tackle, rush the quarterback, and intercept passes and are smart choices to draft.