Running from "the grind" is a phrase popularized by Bay Area rapper P-Lo and producer Cal-A. "The grind" represents the lifestyle of chasing a goal or a certain task. Tasks can include anything from working out to getting work done.
Did you hear about how Adam didn't show up for practice today?
Yeah, he's running from the grind.
staying "on the grind" means to work hard, always be hustling, or otherwise engaged in money-making or woman-procuring activities.
people who were once poor and become wealthy might then become lazy and indolent and spend all day in champagne-filled jacuzzis whereas other newly-successful people might continue to work hard, thus "staying on the grind"
there are many examples from 50 Cent's latest release, "the Massacre", but i'll offer up two:
excerpt from "God gave me style":
A O.G. told me God's favorites have a hard time
You out the hood, that's good now stay on the grind
Chorus from "Bitch get in my car":
I got no pickup lines
I stay on the grind
I tell the hoes all the time
Bitch get in my car (Bitch get in)
I got my 64, ridin' on Dayton spokes
And when I open that do'
Bitch get in my car