What is FLEX in fantasy football?
A FLEX is a starting-lineup slot that can be filled by a running back, wide receiver, or tight end — your choice each week.
FLEX
The flex is an open starting slot you can plug any RB, WR, or TE into, letting you start your best matchup regardless of position.
If your roster already starts 2 RBs and 2 WRs, the flex lets you add a third RB, a third WR, or a second TE — whoever you project to score most that week. Most standard lineups include one or two flex spots, and they're where a lot of week-to-week strategy lives.
Because the flex rewards depth, drafting a strong bench of startable RBs and WRs gives you more good options to rotate through the flex as matchups and injuries change.