There are any number of possibilities so it really all depends on what you have seen in and around the plants. Some caterpillars will do similar damage but depending on fencing and how low to the ground the fruit are, there are voles, mice, rats, squirrels, gophers, etc. If the fruit are exposed and near the top then birds are a possibility.

Truly only you can determine the real culprit by carefully examining the plants for caterpillars and watching the garden closely for varmints. If you see one then there are likely more.

Dave

Tomato worms... those big ugly green ones..ck real close. look for little black specks(poop) on the leaves below where they have been eating. That will help with locating them.

The "long grooves" look like bad concentric cracking. Ants, fruit fly larvae, or other pests will take advantage of openings in the skin after the tomatoes crack. Or possibly a combination of pests and rot.

If you're having bad problems with cracking due to crack-prone varieties + crack-promoting weather (heavy rains, alternating dry weather and heavy rains, often with unusually hot or cold temps, etc.), pick the tomatoes early when they first start changing color and finish ripening them indoors.

If the damage is happening when the fruits are green, and the margins around the damage are smooth, the most likely culprit is caterpillars of some kind. A Bt spray will help with that.

consider squirrels and/or rats

Possibly rats, I had a few in my garden last season who took a liking to my tomatoes.

If I'm not mistaking, your first picture seems to have caught the culprit in action: look at the top, to the left of the stem.

I have same problem. All the big ones are eaten. Put some fencing. I wish there was a nice scarecrow kind of thing to detect motion and scare these critters at night.

Not sure about your location, but fruit flies have been very bad where I am. They will get into any flaws in tomatoes, including cracks from rain/weather, and cause rot and liquefaction in parts of the fruit. They're a problem every year around this time where I am.

I am having same problem. Every day I loose quite a few green tomatoes. I had put a chicken wire cage on one of the raised beds. Those tomatoes started turning red and then boom last night someone ate the biggest one I had. Feeling so bad right now as I don't know what else to do. Have setup a trap for the rat but nothing there. It can't be squirrel or opossum like I thought before as they can't get through the cage.