if you make your sole living from sports, anything more than 1% of your bankroll per play is usually risky if you're a grinder (between 1,000-2,000 plays per year on average)
if you're a pro who only bets a few games a week, then i'm sure 2-3% of bankroll would be okay (but i'm just guessing cause i've never tried that, i bet well over 1,000 plays per year myself)
if you're a part-timer or just doing it for fun, 2% of bankroll is an acceptable risk. but don't change your bet sizes around, keep theme the same....
that's where most guys go wrong. if you're bankroll goes up by 50%, then you can resize to the new 1 or 2% mark (whichever you're using)
personally, i have a very high risk tolerance (you should see my stock portfolio, heavy into junior resource stocks in canada, etc.) but when it comes to gambling...
1% of my bankroll, each and every play. no exceptions. always worked great for me.