The bug
Punching a dolphin (I know it's rude, sorry!) are suppose to follow you and attack you, just like zombie pigman and wolves. Which they can also do in their groups.
However, punching it in the 1.14 snapshots and pre-releases, they seem to don't follow you anymore, but actually still attack you when you touch them.
To reproduce:
1: Punch the Dolphin (again, sorry 😞 )
2: Watch it not follow you.
3: Go towards the dolphin you attacked and watch it still hit you though it isn't following you.
Can confirm for 20w11a, they don't seem to "target" the player that hits them.