*I would like to note that I am not a veterinarian, and I will always recommend seeing a vet for any serious health conditions or injuries. *  

Bumblefoot

Bumblefoot is an abscess in a bird's foot.  This is caused by an injury to the skin on the bottom of the foot. A nick or cut can allow bacteria (staphylococcus) to enter the wound.  Pus begins to develop and often becomes a hard painful lump.  In severe cases I recommend seeing a veterinarian to have it removed. 

Angel Wing