Egg with no shell?

I don't know which of my four laid it because I found it in the yard just a few minutes ago. Any suggestions?

causes for Soft Egg Shells and Shell-less Eggs

There are three common causes of soft-shelled and shell-less eggs. The most common cause is a lack of calcium in the hen’s diet. A tremendous amount of calcium is used to form each eggshell. A fascinating egg fact: An eggshell is comprised of 95-97% calcium carbonate crystals. Hens need to have a steady supply of calcium to replace what is lost through egg production. At the first sign of soft-shelled eggs, consider feeding your flock more calcium through either crushed oyster shells (at any feed store) or feeding hens their own eggshells. When recycling eggshells back to your flock it is essential to first bake and crush the shells. This step prevents chickens from recognizing and associating eggshells with food and forming egg-pecking habits.
Dietary imbalance is the second most common cause. Chickens love treats. It can be very tempting to over indulge your birds’ desire for treats and get rid of unwanted leftovers and kitchen scraps. However, feeding too many treats usually results in the birds not eating their layer feed, which is balanced with protein and calcium. Ideally, only 20-25% of a chicken’s diet should come from treats. If you are finding soft-shelled or shell-less eggs in your flock, consider adjusting their diet.
The third most common cause is bullying. Some flocks suffer from terrible henpecking issues. Tormented, subordinate birds are emotionally and physically affected by being constantly attacked. A henpecked bird will often lay misshaped eggs. And you may wonder why have my chickens stopped laying. These problems can all be due to stress. To a certain degree, chickens must work out the pecking order among themselves without human interference. However, if the bullying in your flock has become vicious and on-going, you should intervene. One remedy for serious henpecking problems is to use beak bits on aggressive chickens. A beak bit is a plastic ring that is fitted onto a bird’s beak and prevents behaviors such as feather pecking.
If calcium and dietary deficiencies or stress are not at the root of soft-shelled or shell-less eggs in your hen, then you need to consider some of these less common causes. A chicken laying soft eggs can also be caused by; parasites, disease and poor genetics. Lice and mite infestations may stress your hen to the point that she is unable to lay normal eggs or even lay at all. Eradicating parasites can cure soft-shelled and shell-less egg production caused by this issue.
Illness and diseases such as avian flu, respiratory infection, Newcastle’s disease, Egg Drop Syndrome, etc. can also lead to soft-shelled and shell-less eggs. Generally there are no effective treatments for these diseases. Either a disease will clear up in time on its own or it will kill your chicken. A hen that was once ill with these sorts of diseases may not be as hardy a layer upon recovery.
Lastly, genetic defects can sometimes cause soft-shelled or shell-less eggs. A hen simply might have a chronically inflamed or defective uterus that is unable to properly deposit a shell over an egg. Such a genetically deficient hen should not be used for breeding stock. Some chicken sources suggest culling these genetically defective birds. However a backyard hen is often more a pet than livestock and culling may not be palatable.

Thanks for the reply! .. I do have one hen that was recently injured and she was separated and just put back together in the past week and they have been bullying her so it may have been her that laid .. but im not sure ... they have oyster shell available but they do free range alot so maybe that's the problem. Maybe too much outside eating and not enough of their feed ..