Police said that 22-year-old Christopher Sullivan was at a friend's house in the 2800 block of Garner Avenue.
Authorities said two partygoers got into an argument shortly before midnight over NFL teams. During the fight, one man pulled out a handgun.
"We're getting information that he stepped in actually to help his little brother," said Lt. Richard Lawhead from San Bernardino police. "At that time somebody produced a handgun."
Sullivan was shot twice, once to his neck. The gunman fled the home on foot before police arrived.
"I don't have anybody who knows anything," said Sullivan's mother Suzanne. "Please call the police. If you guys are really his friends don't turn your back on him now. He really needs you guys."
Sullivan was taken to a hospital and listed in critical condition awaiting surgery.
"They said he was going to be a paraplegic, he will never walk again," said Sullivan's mother Suzanne.
Sullivan arrived home on Thursday from Fort Campbell in Kentucky after serving one tour of duty in Afghanistan.
His mother said while on tour he received a purple heart after being wounded in a suicide bomb attack last December, and that five of his friends were killed in the attack.
Sullivan's mother said that having her son survive that attack in Afghanistan, only to succumb to gunfire back home, is testing her strength.
"He is an excellent son, and he's an excellent boy," she said. "He didn't deserve this."
His family has put Christmas on hold. Right now the only thing they are asking for is an arrest, and for Sullivan to have a miraculous recovery.
Police do know who they are looking for; they said they have questioned about a dozen people at the party.
If you have any information, call the San Bernardino Police Department at 909-384-5619.