For NFL players, when a window of opportunity closes, another opens – a tampering window, that is.

The NFL's legal tampering window opens on Monday at noon ET, officially signaling the unofficial start of free agency (Wednesday, March 13). For unrestricted free agents testing the waters, this two-day period offers a bit more clarity on their respective markets.

That said, the negotiating window isn't always cut-and-dry. Players have backed out of deals in years past, opting to take their talents – and bank accounts – elsewhere.

For those unfamiliar with the tampering window, what it means and why you should hold off on any excitement of your favorite team signing a big-name free agent, read on:

What is legal tampering in the NFL?

The NFL's legal tampering window is a two-day period prior to the start of the new league year, in which teams can speak directly with other players' representatives and broker deals ahead of the official start of free agency (4 p.m. ET, March 13). The window opens on Monday at noon ET and closes at the start of free agency.

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To combat the amount of backdoor deals which were taking place before players would officially hit the open market, the league instituted the legal tampering period allowing players' agents to speak with interested teams in 2012. That means you'll hear a lot of players agreeing to deals with new teams ahead of Wednesday.

That said, the deals that are struck during the legal tampering period aren't official until they are signed, which means players can back out of any deals made in the window. While that's not necessarily a common occurrence, it has happened in years past.

There are some restrictions, however. Players cannot visit other teams' facilities during the tampering window. They cannot speak directly with other organizations' front offices (that's left to the agents).

The NFL describes the negotiating window as the following: "The purpose of the two-day negotiating period is to create a level playing field in the competition for Unrestricted Free Agents by permitting clubs to negotiate with the certified agents of such players concerning all aspects of an NFL Player Contract."

When does NFL free agency start?

NFL free agency begins on Wednesday, March 13 at 4 p.m. ET. Players can officially sign deals with new teams at this time, the start of the new league year.

Top NFL free agents 2024

According to USA TODAY's Tyler Dragon, here are the top 10 players who will be available ahead of free agency (as of March 10):

1. Saquon Barkley, RB
2. Justin Simmons, S
3. Kirk Cousins, QB
4. Christian Wilkins, DT
5. Derrick Henry, RB
6. Josh Jacobs, RB
7. Tyron Smith, OT
8. Chase Young, DE/OLB
9. Danielle Hunter, DE/OLB
10. Calvin Ridley, WR

For the complete list of top 50 players entering free agency, click here.

NFL free agency predictions

Per USA TODAY Sports' Jim Reineking, here's where some of the top free agents in the NFL may sign in the coming week:

1. Saquon Barkley, RB: Bears
2. Kirk Cousins, QB: Vikings
3. Christian Wilkins, DT: Bears
4. Derrick Henry, RB: Ravens
5. Josh Jacobs, RB: Texans

For the complete list of free agency predictions ahead of free agency, click here.