The Ravens placed running back Jeremy Langford on practice squad Injured Reserve, according to a team announcement. In his place, the team has signed running back John Crockett. 
Langford, once the top ball carrier in Chicago, was released in early September. Somewhat surprisingly, he was not claimed on waivers by any of the league’s other 31 teams, making him a free agent. He joined the Ravens’ taxi squad before the start of the season and even spent one game on the roster before being cut and re-signed to the practice squad.
Langford, 25, has 28 games of NFL experience to his credit. Between 2015 and 2016, Langford accumulated 737 career rushing yards and ten career rushing touchdowns with an underwhelming 3.5-yards-per-carry average.\
Crockett, also 25, has only two NFL appearances on his resume, both coming with the Packers in 2015.
What is the difference between the 2 IR ?