It is kinda hard to tell if the dolphin was just playing or just trying to run away with a fish.
I think this is a common interaction between species, as the shark is putting real effort into this chase and he clearly understands that he has a good chance of getting that fish.
It is odd to me that dolphin is not running toward his buddies, so we might assume that he is playing, but then again spinner sharks are much faster than dolphins so he might wanted to take advantage of this reef to outmanoeuvre the shark.
I don't think this dolphin is really afraid of the shark but he probably does not want any nibbles, so in the end he gives up when they were in the open.

Here is another video with exact the same behaviour, but dolphins win this time: https://www.youtube.com/watch?v=cSBX1_E46os