70%

I am a native English speaker and I have never heard this phrase before, so don't worry it's not you!

Meaning in a race, where people normally run to win, a person might be so far ahead, or the race might be so lopsided that one could win by walking.

Someone answered already, but I just wanted to point out that I loved your use of "grok". I'm native English speaking and I could only guess what "win in-a walk" could mean through context. You're doing great