Kristopher Oswald, 30, had been working at a Walmart in Hartland, Michigan, for about seven weeks when the incident occurred.
Oswald, who had been working the overnight shift stocking pet supplies, was eating food in his car while on a break, when he suddenly heard the sound of a woman screaming.
He went to investigate, and came across what appeared to be a man pushing a woman up against her vehicle.
When Oswald asked the woman if she needed help, the man abruptly attacked him with a series of blows to the head.
Oswald said the man continued punching him while yelling, "I'm going to kill you."
It was then that Livingston County Sheriff deputies arrived on the scene and stopped the brawl.
According to Oswald, he was summarily terminated the following day for violating company policy "on his lunch break."
It remains unclear which policy Oswald violated, as Walmart's guidebook does not explicitly prohibit employees from assisting individuals in apparent danger or exercising self-defense in the face of bodily harm.
Despite the negative outcome, Oswald told the news station he would do it again. "I will always do the right thing," he said.