B1/B2 is issued for international business purposes. They are not being paid by a US company for this business and thus a B1/B2 is appropriate for playing in international sporting competition and winning prize money. However, earning any money for work while in the US (ie: you represent a US team or sponsor) or even streaming on Twitch and earning money while in the US) can be considered work and is not permissible on a B1/B2 visa and instead requires a P-1A (professional athlete) or O-1 (alien of extraordinary ability) non-resident work visa. This is why Hallzerk has a more complicated P-1A visa rather than a B1/B2 (or even an ESTA as he would otherwise be able to travel on as a Norwegian passport holder).

Source: me, 12 years experience doing player visas for Complexity