An unlikely duo: Ryan Mattheus and Katy Perry

When it comes to picking a walk-out song, most major league relievers select something intense, something that will get their adrenaline flowing and pump them up as they jog out to the mound. Longtime Padres closer Trevor Hoffman used AC/DC's "Hells Bells" as his walk-out music. Mariano Rivera is famous for his use of Metallica's "Enter Sandman". Ryan Mattheus goes a different route. A very different route. You might have noticed that when the Nationals call on Mattheus, their 28-year-old reliever, in the late innings of a game, the music that blares through the speakers at Nationals Park is not heavy metal or up-tempo rap. Instead, pop singer Katy Perry's "Firework" is the selection. How did that come to be? Why did Mattheus pick a song that's beloved by pre-teens as his pump-up music? Turns out, it started last year as a joke between Mattheus and then-teammate Cory Van Allen when the two were playing for Double-A Harrisburg. "We were just out after a game one time, and we heard the song," Mattheus said. "It was early in the year, so neither of us had a walk-out song yet. I'm like, 'Dude, I'm just gonna do this. Katy Perry.' And it was kind of fun, kind of a joke. And then I got (to the majors), and I had had success using it, so I was like, 'I gotta do it.' "I was kind of nervous about it at first, like 'What's everyone going to think when I run out of the bullpen with "Baby, you're a firework" playing all over the stadium?' I kind of went with it, and last year I didn't give up a run at home, so this year I came back (with it)." Unfortunately, the Katy Perry home scoreless streak ended on Monday when he allowed a run in the eighth inning of a win over the Astros. Mattheus says now that the magical ride is over, he's considered switching his song, but hasn't come to a decision just yet. "I'm kind of debating it," Mattheus said. "But I think it's fun. The fans now are starting to get a little reaction out of it. It's just a fun song, kind of a joke. That's why I used it." But what about the whole intensity factor that leads most relievers to pick a song that's a bit - how should I say this - heavier? Doesn't Mattheus worry that the pop song might snap him out of the fierce mound mentality that relievers try to create? "Yeah, see, I think I'm over the top the other way," Mattheus said. "I'm always intense, and when I'm in there anyway, I feel like if I have that song, I can kind of calm down a little bit, maybe. Make me laugh and lighten up instead of getting more intense. It's just fun." As you might expect, Mattheus' teammates have gotten on him about the song a little bit, singing it as he walks by and making Katy Perry jokes from time to time. But Mattheus, who always seems to have a smile on his face, takes it all in stride. "They give me a hard time about it all the time," Mattheus said. "Gio (Gonzalez), he hadn't heard it yet, so (Monday) night he was singing it to me. He was going, 'Baby you're a...' It was funny. He loves it. I just hope that's the reaction from everybody."