I made a bet on this Canadian Tennis player, Bianca Andreescu a few months ago (Pre-Covid), I won like 20 bucks. Next, round I lost. Then I just started playing black jack and things are more consistent. However, it's not big money. I would say you better know A LOT about the sport you are betting. I don't know anything about Tennis, I just saw her in the media and got lucky. One time only.