The Miami Dolphins are signing Raheem Mostert (RB/KR, Purdue) to their 53-man roster off the Philadelphia Eagles practice squad today.— Brett Tessler (@TesslerSports) September 14, 2015
Mostert, an undrafted free agent out of Purdue, led the NFL in the preseason in yards from scrimmage and total yards. He beat out by Kenjon Barner for the last spot on the Eagles' running back depth chart, but Philadelphia was hoping to be able to keep him on the practice squad during the year.
According to NFL rules, players on the practice squad for any team are free to negotiate a contract with another team to be signed to the active 53-man roster. The player can be released by the new team at any time, but will receive three game checks and account for a spot on the 53-man roster for three weeks after being "poached." There are rules limiting when a team can sign a player from an upcoming opponent's practice squad, but Miami does not player Philadelphia until Week 10, well ahead of the limitation.
(H/T Bleeding Green Nation)