You googled it. Hmm.. That has as much validity as you saying "Because I said so".
It's a stat that ESPN created in 2020. Contrary to their claims that it's objective, it's not. It's subjective. Because they can't know what the offensive player's assignment is on each play. They also don't tell how they account for TEs or FBs. Not to mention that there are designed run plays that allow a defender up field to take them out of the play. When an article explaining how it works says " It does this by using a large set of rules based on relative distance to the runner, relative velocity to the runner and
many other more complicated measures", they're telling you they don't think you're smart enough to understand. They're also telling you that they're putting their finger on the scale to make it work.
We created better metrics to measure run-blocking and run-defending. Here's how our model works, and what these stats can do.
www.espn.com
Ask yourself this.. If RBWR was such a great stat, why don't they list it on the player pages on their own web-site the way they list sacks, stuff yards, etc.
Out of curiosity, I went to go look at Ben Brown's player page on ESPN. Nothing. Not Stats at all. So, to say that Zion Johnson is the 2nd best because that's the list that ESPN put out is nonsense. Especially when they don't make the results for each player available.