Ahmad Bradshaw remains the Giants' starting running back, but he's had his own problems this year with foot and neck injuries, and after Brown's injury the only other back on the roster was rookie David Wilson. Wilson is likely to be Bradshaw's primary backup, but since running backs are so fragile it makes no sense to carry only two.
Torain played eight games and started four last year for the Washington Redskins. He also played for the Redskins in 2010 and the Denver Broncos in 2008. He has not played in an NFL game this season. He's the guy of the two who's got starter's experience and, if he shows an ability to stay healthy and Wilson struggles, Torain would be the best fit for the sort of role Brown had been playing.
Lumpkin was with the Seattle Seahawks this year but did not appear in any games before they released him Sept. 18. He played two games for the Green Bay Packers in 2008 and a total of 27 for the Tampa Bay Buccaneers in 2010-11. His most significant playing time came in 2011, when he had a total of 31 carries for 105 yards as Tampa Bay's backup.
To make room on the roster for their two new backs, the Giants put Brown on injured reserve/designated for return and released offensive lineman Selvish Capers.