The baby may not have been strong enough to wiggle itself around to peck the shell open further, or that the shell contents dry out too quickly and then the chick adheres itself to the inside of the shell and unable to move.
If this is indeed what happened, make sure mom has enough access to bathing or showering while she is incubating as moisture is crucial.
Also, there are things you can do if this should happen again. You can gently remove a tiny bit of the shell around the babies head,so the babies head is free, or apply a little bit of your own saliva into the hole of the egg. The sailva is warm and slippery, sounds yucky, but it works. Put the egg back in the nest, and keep a close eye out. These two things can be done and will work, but only if the chick shell dryed out, and this is not another issue going on, like disease.
If this is indeed what happened, make sure mom has enough access to bathing or showering while she is incubating as moisture is crucial.
Also, there are things you can do if this should happen again. You can gently remove a tiny bit of the shell around the babies head,so the babies head is free, or apply a little bit of your own saliva into the hole of the egg. The sailva is warm and slippery, sounds yucky, but it works. Put the egg back in the nest, and keep a close eye out. These two things can be done and will work, but only if the chick shell dryed out, and this is not another issue going on, like disease.