I wouldn't know from personal experience, but I bet LoneJack(a member of this forum) could tell you all about it. He's had problems with possums and raccoons eating his melons recently. I wouldn't be surprised if you had the same culprit.

Or even a groundhog.

I can't really ID just by the picture, are there any claw marks around the edge of the area that's been eaten? Raccoon claws have a very distinctive pattern that they leave while holding the fruit when they are munching on a melon.

Looking at the smaller teeth marks around the perimeter of the wound it looks like it might be a rat.

I doubt that the fruit will make it long with the open wound. It will invite other pests in to sample and rot fairly quickly. You might want to sacrifice that fruit so others may live to a ripe old age.

We have a squirrel doing something like this.

I usually leave the partially eaten fruits in the garden and hope the critters will go for them instead of starting on others. Also, I never eat those that have been chewed by rodents because of the possibility they may have spread diseases onto the flesh through their saliva or urine. Just not worth the risk.

The squirrels are bad in that they take a bite and then leave the fruit. Then they bite the next one and so on.

That's really odd I'd lean to voles or mice