The die-hard Red Sox fan, who is now the team's head groundskeeper, was hit by a car while walking into a McDonald's. His once promising baseball career was over.
But Mellor didn't let that get in the way of making other plans.
"I think I'm the luckiest person in the world, I never would've met my wife, I have two amazing daughters, I have a career I enjoy so much," said Mellor.
That career now includes his best furry friend, Drago, a German shepherd.
"Other than my wife, he's my best friend," said Mellor.
Mellor and Drago, his service dog, are inseparable.
"He's trained to help me with symptoms and triggers and so he can do anything from help me wake up from a nightmare to help me with mobility and if he senses anxiety he has tasks to train to get me to refocus my energy on him," said Mellor.
After his first accident, Mellor was hit by a car two more times and has undergone 43 surgeries. He says the pain was both physical and emotional.
"I had horrific 3-D car crash nightmares every night for 29 years, had flashbacks during the day when I heard revving car engines, smelled exhaust," said Mellor. "If I smelled McDonald's french fries I had flashbacks because the first time I got hit by a car was at McDonald's."
After living with nightmares for nearly 30 years, Mellor was eventually diagnosed with PTSD.
"The first paragraph listed 12 symptoms of PTSD and just reading them, chills went through me and tears started coming down my face," said Mellor. "While it scared me, it gave me hope, I realized I had 10 of the 12 symptoms."
It's been a long journey to the big leagues for Mellor, and he's working the World Series side by side with his perfect teammate.
After Drago fathered a litter of puppies born this summer, Red Sox pitcher Rick Porcello adopted one of the pups as well as infielder Ian Kinsler.