I'm not entirely sure what fits your definition of "normal laws" but if it loosely translates to not directly harming other individuals I would imagine that match-fixing would fit your criteria. I haven't personally indulged so I cannot directly provide you with much related information but I'd say betting on fixed matches is the least illegal and harmful thing one can make money off of on the DW.
If I were to partake in match-fixing, I would probably find a reputable site, build a reasonable amount of capital, and just invest my money into legal things that provide passive income after.