SEATTLE -- A class from Bellevue's Highland Middle School expected to spend Thursday morning at Safeco Field starring alongside the Mariner Moose in an anti-bullying public service announcement.

Students had no idea their true co-stars were Mariners ace Felix Hernandez and Seattle-based rapper Macklemore.

The American League All-Star pitcher and Grammy Award winner, respectively, teamed with Seattle-area middle schools to launch #ChangeTheGame, a campaign aimed at stopping physical and mental bullying.

Hernandez and Macklemore surprised students by hiding while the Mariner Moose clumsily botched two unsuccessful takes. Students stood idly near home plate, not sure what to do. Then Hernandez, in full uniform, jogged out of the first-base dugout. Moments later, Macklemore followed.

"It means a lot," Hernandez said after wrapping up filming. "It means a lot, because I'm part of the Seattle Mariners and the community has to hear something from me. It's really important, because [kids] look up to us when we're on TV, and when we do this, they're going to hear it."

In the 30-second PSA, which will be distributed to radio and television stations throughout western Washington, the two superstars urge students to "be kind, stay positive and support each other." It ends with the line, "Together, we can change the game."

At Safeco Field on Thursday, the phrase "Stand up to Bullying" flashed across the center-field scoreboard before tweets with the #ChangeTheGame hashtag rolled across the screen.

As part of the campaign, posters and activity guides will be handed out to teachers. With the help of their parents, students can go to mariners.com/changethegame to take an anti-bullying pledge and enter to win a contest to meet Macklemore and Hernandez before the Mariners play the Yankees on June 12 at Safeco Field, which is Macklemore Bobblehead Night.

"It's an honor to be working with the Mariners and Felix Hernandez to help spread a message of individuality to our area schools," Macklemore said in a press release. "We hope to encourage our youth to feel free, to be themselves and to take care of each other along the way."

Hernandez, meanwhile, was his typical, outgoing self. He posed for at least one "selfie," smiled and gave high fives. He spent approximately a half-hour with the seventh- and eighth-grade students from Highland Middle School's elective class, AVID, which is an acronym for Advancement Via Individual Determination. Consisting of kids who must overcome socioeconomic and English-language barriers, the class focuses on developing leadership, reading, writing, collaborative and organizational skills to improve their chances of attending college.

Hernandez and Macklemore drew screams and cheers when they walked out of the dugout.

"I was like, 'Oh my God,' we were just taking pictures with the Moose!" exclaimed seventh-grader Matai Patten.

Though Hernandez jokingly denied it afterward, Macklemore drew the loudest student ovation when he emerged in a throwback jacket and sunglasses. The local music artist, after all, did take home four Grammy Awards in January for his 2012 album, "The Heist." It includes the song "My Oh My," which pays homage to late Hall of Fame Mariners broadcaster Dave Niehaus.

"[He] was more surprising, because Felix is on the baseball team, but Macklemore just came out of nowhere," said Matai's sister, eighth-grader Jazmine Patten.

When the Mariners first approached Hernandez to be face of their campaign, he didn't hesitate.

"[The club] talked to me about it," Hernandez said, "and I was like, 'All right, let's do this,' because it's important for me to give a message to the kids to just be themselves. I think they have to feel free and safe in school."

For #ChangeTheGame, the Mariners partnered with the King County Sexual Assault Resource Center, Committee for Children, U.S. Department of Justice, United States Attorney's Office, Western District of Washington, DOJ's Community Relations Service and Copacino+Fujikado.