Buck with Lump on Jaw

I occasionally feed the deer in my Texas backyard protein pellets and corn, and have noticed a large and otherwise healthy looking buck with a huge tennis ball sized lump outside his jaw. He seems very hungry and nibbles for an hour sometimes. I've also seen him occasionally with this pouch 'deflated.' He is a large, calm, handsome buck, and I feel bad for him. Does anyone have any idea if this is a disease, disfiguration or just a strange habit? I would like to help him, if he needs it. Thanks!

Thanks, I appreciate your response - it leads me to another question... We've had several droughts the last few years, with temperatures in the triple digits. To help the deer, I keep fresh water out in the summer. Do I need to worry about the other deer becoming infected because of this buck? I would hate for harm to come to any of these critters because of my water trough!

Thanks, hhgaryh, that puts my mind at ease. They are such a joy to watch... I wouldn't want to accidentally harm these beautiful animals!