The Nationals hope that the 19-year-old Harper will be the next great thing in baseball and that he'll lead the franchise for years to come.
First, though, there was Monday.
Mattia, 34, is a financial analyst for a Department of Defense contractor. He's also a Nationals fan, and a dedicated softball player.
On Monday, Mattia was playing on the National Mall with the Killer Watts, a team made up of employees of The Alliance to Save Energy and some friends. The team is part of the Green League, so named because it's composed of nonprofit environmental organizations, such as the World Wildlife Foundation.
Other Green League teams are the Fighting Green Weasels (American Rivers/ICMA), Gang Green (EPA), Global Swarming (LCV/EarthJustice/PIRG) and Sea Slugs (Greenpeace).
"The Killer Watts made several championship games over the last few years, but if you ask me, it was the 2011 acquisition of me that led them to their first championship last year," Mattia wrote in an e-mail on Wednesday afternoon. "Bryce isn't the only superstar athlete in D.C. I have the distinction of being the only one anyone on any of my teams knows who has hit for the cycle, and I've done it twice."
So what happened on Monday, Lucian?
"I was playing third base. ... Between pitches, my mind was wondering, and I was staring off into nowhere," he wrote. "I spotted a few guys with a small but professional-looking video camera. It's no surprise at all to see a big camera in that area, but I took another look after another pitch and quite quickly recognized that it was Harper. ... A lot of people make a big deal about the hair, but I'm a pretty big Nationals fan. I know what he looks like and was close enough to get a good idea of what I saw."
Mattia whispered to his shortstop that Harper was watching their game.
"Are you serious?" was the reply.
Mattia yelled at Harper to come play catcher.
"The Nats won't let you play there, but we will," he said.
Then someone came up with the idea of having Harper pinch-hit.
"I yelled to the pitcher of the other team to see if it was OK," Mattia wrote. "He said sure, but being down about 20 runs, any runs Harper contributed to would be added to their total."
Mattia handed Harper his bat.
"Man, I've never hit a slow-pitch softball," Harper said.
"I think you'll be OK," Mattia told him.
And when Harper stepped into the batter's box, Mattia grabbed his camera.
Harper caught the first pitch and tossed it back to the pitcher, swung and missed at the second, and launched the third one down the right-field line.
"His did land fair. ... Some people can't seem to tell," Mattia said. "I was next, so I got the bat from him, and when I stepped up, I turned and said, 'This is how it's done' to him. I definitely hit my fair share of homers, but I was only able to hit a line-drive double."
Harper had gone to the National Mall to shoot a promotional video, but it was the video of his two softball swings that went viral. He later posed for pictures and chatted up players on both teams.
"Bryce was a good guy," Mattia said. "Obviously, he's been dealing with increasing celebrity status over the last few years. I think what he did was a total treat for a lot of us there."
Mattia welcomed Harper to Washington and mentioned that he lived near Nationals Park and went to a few games a year. Twice a year, he invites a large group to his apartment to have some beers, then the group walks to the park and takes in a game.
This year's invitations will feature the photo of him and Harper.
Lucian and Bryce invite you to the next Nats Bash.
"Basically, he conducted himself like most of us regular folks would want celebrities to conduct themselves ... like they're not a celebrity," Mattia said. "He was just hanging out on the Mall like the rest of us. I think it was a really cool thing that I've never heard of any athlete doing ... ever. I was slightly disappointed that I didn't have any Nationals gear with me for him to autograph."