CHICAGO -- Tommy Nance remembers how his dad used electrical tape to create a makeshift strike zone on the netting they put up in their California backyard. He remembers the bucket of baseballs there at his side.

"He always gave me the tools that I needed to be able to take it as far as I could," said Nance, leaning on the netting at Oracle Park as he spoke during the Cubs' recent trip to San Francisco.

Nance's story on its own is a baseball miracle.

Tommy John surgery after his senior season at Santa Clara University. Undrafted. A tryout that led to a roster spot with the Windy City ThunderBolts in independent baseball. A backyard throwing showcase that led to a chance with the Cubs.

And then there was the phone call home in May, when Nance got to tell his parents, Mark and Susan, that he was called up to the Major Leagues. Nance said it was a "proud dad moment" for Mark, but it was so much more for their entire family.

That Mark is here to watch his son's big league dreams become reality is also a kind of miracle. He was diagnosed with amyotrophic lateral sclerosis (ALS) -- commonly known as "Lou Gehrig's disease" -- nearly seven years to the day of Tommy's MLB debut.

"When he first called me, I was like, 'Are you kidding me?'" Mark Nance said in an interview with Marquee Sports Network. "I was in shock. Tears. My wife, Susan, and I were just like, we hugged each other. And I was like, 'Are you kidding me? You made it. I always believed you could do this.'

"To see him work so hard all these years and never give up, always trying to move forward, it's amazing."

Tommy Nance feels the same about his dad.

On May 22, 2014, Mark Nance -- a veteran of the Air Force and retired firefighter -- learned that he had ALS and was working through how to be honest and positive with how he explained the situation to his kids. That same weekend, Tommy headed home from college for a surprise visit.

Tommy returned to an empty house, phoned up his dad and asked what was going on.

"It was the hardest thing I ever had to do, was tell my family that I had ALS," Mark Nance told Marquee. "I told everyone and decided, 'Don't worry, kids. I'm going to fight this. Don't be sad. Don’t be unhappy. Don't be bummed. I don't want anyone to feel sorry for us. I want to fight this.'"

"I remember finding out, it was just a lot to take in," Tommy said. "I didn't really know anything about it, what it meant, anything like that."

ALS is a disease that attacks nerve cells and results in a rapid decrease in motor functions and muscle control. The average life expectancy of the illness is two to five years. According to ALS.org, more than 5,000 people each year are diagnosed with ALS and the average out-of-pocket cost is roughly $250,000 for families.

Jon "Boog" Sciambi, the Cubs' play-by-play voice for Marquee Sports Network, helped form Project Main St. to help those impacted by ALS. The nonprofit organization was started by Tim Sheehy and a group of close friends (including Sciambi), before Sheehy succumbed to the disease in 2007.

"I would love our charity to go away," Sciambi said recently. "That would mean we cured the disease. In the meantime, I'm passionate about the fact that you've got to raise money."

Mark Nance was hesitant at first to tell his own story, because he did not want to take any attention away from his son.

Tommy Nance's performance this season has been a great development for the Cubs. The 30-year-old rookie rattled off a dozen scoreless appearances to begin his MLB career. In the process, he helped stabilize what has developed into one of baseball's best bullpens.

"I don't want to take anything away from him," Mark said.

The way Tommy sees things, though, his success is directly linked to his dad. Mark Nance never forced his son to play baseball, but encouraged him and stoked that inner fire. And now, Tommy continues to be inspired by how his father has fought ALS.

And both father and son understand that telling Mark's story can continue to raise awareness about ALS.

"He doesn't want the spotlight on him," Tommy Nance said. "But I think he saw a good opportunity to, at least, if someone's struggling with it, to see that he's living with it and staying positive. I think he saw that as a perfect opportunity to speak about it."

When the Nance family learned of Mark's diagnosis, pitching in the Majors surely felt like a pipe dream. As small doors of opportunity began to open for Tommy, however, he never felt any pressure to stay home rather than chase that goal.

Mark Nance would have it no other way.

"He's always just wanted me to pursue my dreams regardless of what he's going through," Tommy said. "I wanted to make it a point to help out and be there with him, of course, but he still would've been like, 'No, go chase your dream.'"

Tommy called the support he received from his family through his journey "unmatched," which has made this season even more rewarding. He debuted on May 17 with a strikeout of Washington's Josh Harrison, and was able to have family and friends in Wrigley Field for a stretch of recent games.

That included on June 2, which was the first-ever Lou Gehrig Day held by Major League Baseball. The day was meant to continue to raise awareness and money to battle ALS.

And when Tommy Nance took the mound at Wrigley Field, he was able to spot his parents in the stands.

"To watch him just feel so comfortable up there," Mark Nance said, "I'm like, 'How can you do that?' I'm amazed. That's who he is. He never quits. He wants his dream.

"That's what I always try to tell my kids, is, 'I want to keep feeding your dream, your passion.' Follow your passion."