https://sussexwildlifetrust.org.uk/news/dolphins-the-good-the-bad-and-the-ugly

Dolphins are known to attack and kill baby dolphins. It is understood that this is because males see new calves as “competition”, so may try and see off the baby, so that the mother is free to make more babies.

And male dolphins are ruthless when it comes to mating. Males can form “gangs”, isolating females from other pods.

You’ve probably seen footage of dolphins playing. However, sometimes it may be that they’re 'playing' with other animals. A well-known example is a group of dolphins using a baby shark as a make-shift volleyball.