NBA - Main

Friction is the force of two objects sliding against each other creating resistance. Tatum had forward momentum when he dunked the ball. He held on to the rim to stop his momentum going any further, but had momentum swinging backwards. If he just held on flat, he would keep swinging back and forth until he comes to a stop. This takes too long and he wanted to come down faster but in a safe landing position, so he swung his momentum up by lifting up on the rim, shifting the direction he was going so he could stop faster and land safely.

You’re right that friction counters momentum if it’s strong enough, but the lower half of his body kept swinging. There’s no friction down there to stop him, so he adjusted up to shift that momentum perpendicular instead of horizontally. Then gravity did the rest and brought him down straight on his feet. If he had let go while still swinging horizontally, he could have landed on his back or stomach. But sure dude, you’re making yourself look like an idiot, but I’m an idiot now because I’m entertaining you.