Maples learned an important lesson that day.
"I think it was my preparation," he said. "In high school, you could get away with not being focused. In pro ball, you have to be focused on every pitch, you have to be locked in -- with everything, from [pitchers' fielding practice] to running poles."
The 19-year-old right-hander got another reality check this offseason when he spent a month at the Athletes Compound at Saddlebrook near Tampa, Fla., for an intensive preseason training camp. He took part because of an exclusive arrangement between Athletes Compound and CAA Baseball, which represents him.
The days started early -- breakfast was ready at 6:30 a.m. -- and were long, including conditioning, injury prevention exercises (known as pre-hab), medicine ball activities, yoga and weight lifting. The Cubs had given Maples an offseason program to do. The work at the Athletes Compound took it to another level.
"We did a lot of stuff the Cubs were doing and we go beyond that," Maples said in an interview this week. "It's really specialized down here. I think because it's a smaller group of people -- we have maybe 10 pitchers -- and we can select what works for me."
The focus, according to Jason Riley, 37, director of sports performance for the camp, is to educate the athlete on the physiological and psychological aspects of the game.
"My job is not to be a baseball coach," Riley said. "My staff's job is not to be a baseball coach. It's to apply movement that they'll see on the baseball field, and how we can make those movements more efficient and reduce the risk of injury with those movements and let the baseball coaches work on the technical mechanics and work on the release point."
Maples, who ranks sixth among the Cubs' future stars on MLB.com's Top 20 Prospects list, may have been taken in the 14th round, but he was projected as a first-round pick. Several teams felt he was committed to college to play football and baseball. It was an option Maples seriously considered. After the Draft and graduating from Pinecrest High School in North Carolina, he wanted to take the summer off and just "be a kid," but his mother urged him to go to summer school at the University of North Carolina. He worked out with the football team.
"She was smart -- I give her a lot of credit now," Maples said of his mother. "That was good that I got to experience a little bit of college. I got to base my decision [on whether to sign] on that five weeks of school, and I was playing football, too."
A punter and kickoff specialist, he practiced with the UNC squad. On Aug. 13, he met with the football coaches who offered him a full scholarship. The next day, he flew to Chicago to meet with the Cubs and signed a $2.5 million deal to play baseball. It was the largest bonus for a player selected after the second round.
"It was a whirlwind," said Maples, who was 9-1 his senior year at Pinecrest.
Maples got an assist from his high school baseball coach, former big league pitcher James Baldwin.
"He talked to me, calmed me down and made me feel better about the situation," Maples said of Baldwin, who pitched for seven teams, beginning with the White Sox in 1995. Baldwin's son, James III, is now in the Dodgers' system as a center fielder.
There were some NFL players prepping for the combine at the Athletes Compound, and Maples admits he picked up a football and ran some routes.
"I had my time," he said. "I think I made the right decision."
He's looking forward to talking about the pros and cons with other two-sport Cubs like Jeff Samardzija, who was an All-America wide receiver at Notre Dame, and Matt Szczur, who was a wide receiver at Villanova.
There are differences in offseason conditioning for the two sports. Baseball involves more finesse-type weight lifting; football is more power lifting. There's an emphasis on strengthening the core in baseball. Athletes study video, learn about nutrition.
"We want to maximize performance without risking the potential for injury," Riley said.
Maples trained in good company. Among Riley's clients were big leaguers Derek Jeter, Ryan Howard, Tyler Clippard, Drew Storen, Ryan Zimmerman and Chris Perez.
"It's a very unique situation that we have," Riley said. "You look at Derek Jeter and he's a veteran for 17 some years in the league and Ryan Zimmerman has eight years in the league, so for a guy coming in young out of high school [like Maples], there's so much he can learn that's not part of the typical educational process that we provide.
"You're living with these guys, you see how they take care of their bodies. I think it's a neat opportunity for the young guys to come in and learn the process of what to expect and how to manage your body and manage your life around baseball. It's a really good learning environment."
Maples soaked it all in.
"I've been asking a lot of them about what to expect since this is my first Spring Training," Maples said. "We've been talking about how to pitch to hitters and sometimes we just talk about life. I've learned a lot while I've been down here."
Maples hasn't actually chatted with everyone.
"Ryan Zimmerman is down here," he said. "I haven't talked to him that much because I'm pretty much star-struck."
The Athletes Compound may have prepped Maples with a variety of exercises, but what probably helped him the most was the chance to watch how players like Zimmerman, Storen and Clippard prepare. The four-week camp taught him that he has to commit to baseball 24/7.
"I thought we'd just work out," Maples said. "You don't just 'work out,' you do pre-habs, get massages, do agility in the morning, and all this shoulder work. People don't understand what it's really like."
He heads home Friday for two weeks before reporting to the Cubs' Minor League camp on Feb. 24. Don't think he'll be sleeping on the couch. Maples' father, Tim, was selected by the Orioles in the second round of the 1979 Draft and reached the Triple-A level. The two are devoted to the game. Dillon remembers a backyard workout that lasted more than two hours and well into darkness as he tried to learn how to throw a curve.
He'll arrive in Mesa much better prepared for his first Spring Training. Maples won't forget those first two outings last fall either.
"Any time I'm around guys who have been around the game a long time, I like to listen to what they say," he said. "In instructs, I learned everything from charting pitches to what to throw to this lefty to what to look for.
"Baseball is a pretty deep game, that's what I learned."