Ball, 24, was waived by Denver in early September and cleared waivers, leaving him free to sign with any team.
A second-round pick in 2013 out of Wisconsin, Ball entered the 2014 season slated for major playing time, but suffered a groin injury and played in only five games. He missed the cut in Denver after competing with C.J. Anderson, Ronnie Hillman and Juwan Thompson for time in the preseason. Ball has also been tied to the Browns as a free agent.
Bostick, 26, is currently member of the Cardinals' practice squad. He fumbled a key onside kick as a member of the Packers that allowed the Seahawks to recover and go on to win last season's NFC championship game. He entered preseason with the Vikings and was released after training camp.
The 3–0 Patriots have featured a tandem of LeGarrette Blount and Dion Lewis out of the backfield early in the season. James White and Brandon Bolden are the other running backs on New England's roster.
- Jeremy Woo