A street free agent is a non-college eligible player not currently signed to an NFL contract. They may be available because they were released from their previous team (or did not play the previous league year), and either cleared waivers or did not qualify for the waiver system. Street free agents are free to meet and / or sign with any team they choose, rather than a waived player who can be claimed by the team with the highest priority. Additionally, a street free agent does not affect a team’s compensatory draft pick calculation.
Street free agents are often young players who were not claimed on waivers during a round of offseason cuts, or a veteran player who has too many (four or more) accrued seasons to qualify for the waiver system and is immediately free to sign with any team they choose.
Williams was entering his second year in the NFL with the Bills, and therefore qualified for the NFL waiver system, where he could be claimed by any team that put in a claim within 24 hours. However, no team did so and he became a street free agent, and remains able to sign with any team he chooses.
Hillman, on the other hand, was a vested veteran with at least four accrued seasons on his resume. After being drafted in 2012, Hillman was entering his fifth year with the Broncos in 2016 after signing a one-year, $2 million deal during the 2016 offseason, before he was eventually released on September 3, 2016. He was not subject to waivers as a vested veteran, and was free to sign anywhere. On September 21 he signed a one-year contract with the Minnesota Vikings.
Prior to the free agency period begins, in an effort to create cap space and roster spots, team’s may be inclined to cut more highly paid, veteran players, in a move most refer to as a ‘cap cut’. These players are considered street free agents and immediately eligible to sign with any team prior to the new league year opening. Players whose contracts have expired must move through the typical unrestricted free agent or restricted free agent process based on their number of accrued seasons.