Are you allowed to post someone elses stream??

Sort of a random question here. I see tons of people on youtube just posting someone elses stream up. Like "Bjerg dominates soloq", by some random person. With hardly any editing. Maybe they give a kick back to the player, idk, I mean i would.

But thats my whole question. Can anyone just take like a 10 minute clip from someone elses stream and post it on youtube? And potentially make money off it? I mean i get montages are maybe different, but this is just like a "heres 10 minutes of a pro player" w/ 50k views..