There is an interesting article about running back depth chart of every single NFL team. It is slightly confusing, so I will break it down.
They have each team labeled and next to them is the first string player, the second string player and the third string player. At the end of the row, you will see a ranking. So if we are referring to running backs, you may see RB1, RB2, Flex, leave on waiver wire. This does not make reference to the starting running back, but to the backup running back. It states the value of the backup and what his value is if the starter would to get hurt.
The ESPN article by ESPN’s Mike Clay is constantly updated and reviewed. And there is a breakdown for each position . Take a look if you have lost an important player for a long period of time.