I cannot call this a full-fledged additional income. Sports bets are often made by those who poorly understand the essence of this business)) However, I have living examples of those who successfully make a stable profit. My friend's son is studying in Eastern Europe now. As far as I remember, he places bets using one of the popular sites like this - https://www.ua-football.com/en/betting/bookmakers/11-parimatch/bonus  Such winnings help him stay afloat. Students always need money. But he makes bets without having a special system and relies only on intuition and his own preferences. I wouldn't bet my money that way. It's easier to buy a lottery ticket.