Originally posted by h1a8
That was due to Hulk surprising Surtur and Hulk's downward momentum (movie physics and logic). After that Hulk was no more a threat than an insect. In no way did us viewers believe Hulk could have beaten Surtur after the first hit.The writer showing Surtur not moving 1mm from punches tells us that Hulk is doing 0 dmg points per hit.
Hulk was literally damaging the source of his power when he got flung off. Hell that is probably why he flung him off. He was getting ready to leap up again before Thor told him to stop.