Now that the NFL scouting combine is complete, it's time to look ahead to the next big item on the NFL schedule: free agency.

It's the time when teams looking to infuse a significant amount of veteran talent onto their rosters can do so, albeit at a premium price. It's also the time when teams looking to emerge as contenders can add a calculated piece or two, looking to get them over the hump. In any case, it's a period of frenetic activity, one of the busiest of the NFL calendar, and the one that churns rosters over.

Here's everything you need to know about NFL free agency:

When does NFL free agency start?

The free agency signing period coincides with the beginning of the new NFL league year. This year, that falls on Wednesday, March 13, after 4 p.m. ET. At that time, any player contracts that were due to expire at the end of the 2023 season will formally expire and the NFL league calendar will officially transition to 2024. This is also the time when trades can be officially consummated, even if the framework for one was arranged before the start of the new league year.

Despite the start of the new league year officially marking the free agency signing period, teams also have another tool to enter negotiations with prospective free agents, commonly known as the "legal tampering period."

What is the NFL legal tampering period?

Beginning Monday, March 11, at noon ET, teams are allowed to contact the certified agents of prospective unrestricted free agents to discuss terms and enter contract negotiations. This period runs for two days, until Wednesday, March 13 at 3:59:59 p.m, ET, the instant before the start of the new league year. Contracts cannot be officially executed until the start of the new league year.

During this period, if a prospective unrestricted free agent is not represented by an agent, he will be able to communicate directly with the front offices of interested NFL teams, but he will not be allowed to communicate with head coaches or any member of a team's coaching staff regarding contract negotiations.

When is the NFL franchise tag deadline?

All NFL teams must allocate their franchise or transition tag designations by Tuesday, March 5, before 4 p.m. ET.

Now, once the tags have been designated, teams will still have the chance to work out long-term deals with those tagged players until mid-July. Typically, the mid-July deadline has fallen on July 15, though the NFL has moved the deadline if July 15 falls on a weekend; this year, July 15 is a Monday.

A player cannot become an unrestricted free agent by refusing the terms of the tag. If the player does not sign the tender, he will be unable to join his team, but also won't be fined or penalized for absences. A player can extend his absence into the regular season, but he'd forfeit additional salary for each game missed.

Who are the top free agents available in the NFL?

Ahead of the start of free agency, USA TODAY Sports' Michael Middlehurst-Schwartz ranked the Top 25 available free agents. Here's an excerpt of the list:

1. Chris Jones, DT, Kansas City Chiefs2. Josh Allen, OLB, Jacksonville Jaguars3. Tee Higgins, WR, Cincinnati Bengals4. Kirk Cousins, QB, Minnesota Vikings5. Brian Burns, DE/OLB, Carolina Panthers6. Justin Madubuike, DT, Baltimore Ravens7. Jaylon Johnson, CB, Chicago Bears8. Antoine Winfield Jr., S, Tampa Bay Buccaneers9. L'Jarius Sneed, CB, Kansas City Chiefs10. Danielle Hunter, DE, Minnesota Vikings11. Christian Wilkins, DT, Miami Dolphins12. Michael Pittman Jr., WR, Indianapolis Colts13. Mike Evans, WR, Tampa Bay Buccaneers14. Leonard Williams, DT, Seattle Seahawks15. Tyron Smith, OT, Dallas Cowboys

Click here to view the entire list of top available free agents.

This article originally appeared on USA TODAY: NFL free agency: When does it start? Who's available?