Week old chick is small, lethargic, and not eating

[Brianjtam39]

I bought 4 chicks 5 days ago, and one is suddenly not eating. It is smaller than the other ones, and they run all over it.

 

[Perris]

some fail to thrive, for a variety of reasons. I let nature take its course with chicks.

 

[Justso]

Please post this on the emergencies forum!
This may be an easy fix.
https://www.backyardchickens.com/forums/emergencies-diseases-injuries-and-cures.10/