QUICK ANSWER
A handcuff is the backup behind one of your fantasy starters, usually at running back. If your starter gets hurt, the handcuff can step in and protect your team from losing that production.
A handcuff in fantasy football is the backup to one of your starters, usually a running back. If your starter gets hurt, the handcuff can take over his role.
For example, if you draft a team's lead running back and also draft the player directly behind him on the depth chart, that backup is your handcuff.
Why Fantasy Managers Handcuff Players
Injury Insurance
Running backs take a lot of hits, and top players get hurt every season. A handcuff works like insurance, especially if your starter has an injury history.
A Productive Offense
Not every backup is worth a roster spot. A handcuff is much more valuable on a good offense, where he can step into a role that already produces points.
A backup on a poor offense may not be worth as much, even if he gets the same chance.
A Thin Waiver Wire
In leagues with deep benches, there may not be many good players left on the waiver wire. A handcuff can be a better use of your last roster spot than a player who will never make your lineup.
The Tradeoff
A handcuff may sit on your bench all year and never score you a point. Before you draft one, think about how valuable he would be if the starter missed time, and whether another player could help you more.
Your league's scoring can also change a backup's value, so it helps to understand PPR. For another useful term, see our guide to Opp Rank.