The full phrase is "always be hustlin". That does have a certain context. Not necessarily fraud, but certainly cutting corners, winning at any cost, etc.

See Glengarry Glen Ross for something very similar.

So did I, but outside the context of sports it still mostly means scamming people and/or generally earning money illegally to me. Or maybe a dance.

I don't think I ever saw/heard it used in its startup culture sense until I was in my late 20s or so, probably on this very site (and no, I didn't grow up in a place where "hustling" in the sense of scamming/dealing was common) so the scamming/defrauding/dealing/etc. meaning is what sticks with me. Definitely colors my perception when I see it used for other things.

It's just A Word Meaning Different Things Thing; hustle can mean 'hurry' or something similar to 'sprint,' but it can also mean a side gig that gets you a bit of extra income. The typical connotation is with under-the-table stuff and contraband-y stuff in prisons, though, so you might not expect to hear someone talk about their 'new hustle delivering newspapers.'

Uber is currently running ads on Pandora advertising driving for Uber as "the ultimate side hustle".