Ryan McIntosh knew what he was getting into when he deployed to Afghanistan as an Army specialist in the fall of 2010.

Denise Castelli didn't know what she was getting into when she slid into second base as a University of New Haven softball player in the spring of 2008.

For both, there were great consequences. For both, there were unexpected outcomes.

You might have to look twice to figure out why McIntosh and Castelli are different from the other 250 ball persons at the U.S. Open. They are out there retrieving and throwing, providing towel service to the players, part of a seamless team on each court that keeps play going.

McIntosh and Castelli are the ones with the artificial legs.

McIntosh, 23, had been a top high-school athlete in Rifle, Colo. On Dec. 8, 2010, his unit was walking single-file not far from Kandahar. A soldier at the head of the mission was sweeping for mines in an area known to be dangerous. Each step was treacherous. McIntosh put his right foot down and triggered a mine. He was blown 10 feet in the air and landed in a ditch. He said he never lost consciousness and knew he had lost at least part of his foot.

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His leg was amputated above the knee two days later and he was flown back to Ft. Sam Houston in San Antonio, Texas. Fitted with his first prosthesis, McIntosh said he was walking six weeks later. Determined not to let his life languish, he became Adaptive Sports Coordinator at the base, helping wounded soldiers deal with their disabilities.

"I'm trying to get guys back on their feet as soon as they can and realize that life goes on," McIntosh said. "Live life to the fullest and don't take what happened to you as a negative. Yes, it is a negative, but you have to try to find the positive in it."

In May, McIntosh was competing in the Warrior Games in Colorado for injured, ill or wounded servicemen and women, running track, swimming and playing volleyball and basketball. He said he was told he needed to attend a tennis clinic conducted by the USTA as part of its Military Outreach Program. There he found out about the possibility of being a ball person. He came to New York for the tryouts and made it.

The haunting

McIntosh, who has a wife, Hannah, a son, Kaden, and another baby on the way, was working on an outside court at the Open Monday night when the fireworks went off for the opening ceremony. He said it sent tremors through his body.

"My back was to Ashe Stadium and all of a sudden I heard a couple big explosions and it really made me twitch and relive my accident in 30 seconds," McIntosh said. "It was hard. They kept going off and going off and it kept coming back and coming back. It's difficult hearing blasts."

On Arthur Ashe Kids Day last weekend, children were stepping on their noisemakers.

"The sound is very similar to gunshots when they get stepped on, and that made me jolt a bit as well," he said.

On Court 4 the other day, McIntosh moved swiftly and agilely as part of a team that included Jerry Loughran of Garden City. Between points he removed his blade prosthesis, similar to that of South African Olympic track star Oscar Pistorius, and adjusted it to prevent a sore from developing on his stump that could sideline him.

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When McIntosh came to New York, he got in contact with Castelli, who is in her second year as a ball person. He said she gave him some pointers and pumped up his confidence, though there's no lack of it.

Pain, then gain

Castelli, a 26-year-old from Netcong, N.J., said she suffered a broken right leg sliding into second base. The fracture required surgery to put a bracing rod on her tibia. She said she developed a persistent infection that required a number of procedures and resulted in an amputation below the knee on Nov. 14, 2009.

"Ryan went to war and he knows there was a big risk," Castelli said. "I played college softball and what could I worry about, shin splints or a sore shoulder or something?

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"I was completely lost for a while. Then I realized that all the issues with my leg had come to an end , all the medicines, all the time in the hospital. I could just go home, be with my family, my friends. I could start to live my life."

Still, there was great trepidation. She always had been an athlete but now she had no idea what she could do. A doctor who tended to her prosthesis suggested she go to an event for disabled athletes at Chelsea Piers.

"I had this fear about going there, about being in a room with disabled people," Castelli said. "They had programs for every level of disability. By the end of the day, I was running. It was a complete game-changer for me to meet all these amazing people. I got into softball again, got into the Challenged Athletes Foundation and through that got into the tennis."

At last year's Open, she was selected to work the Serena Williams-Caroline Wozniacki semifinal match at Ashe Stadium. The television broadcast honed in on her.

"At the end, people in the stands were high-fiving me as I walked off the court," Castelli said. "My phone had died. When I got back to the hotel and charged it, it exploded . . . My Facebook page was loaded."

As a consequence, she has become a motivational speaker through the Challenged Athletes Foundation, appearing at USTA and corporate events and speaking at high schools. In May she spoke at Commack High School.

"The next day the athletes held a car wash and donated the money in my name to the foundation," Castelli said.

Back to the future

For both, life has moved way beyond their tragedies, way beyond their prosthesis. McIntosh is talking about returning to combat if he can pass Army standards.

"My brother Michael was in the Marine Corps in 2004-2005," McIntosh said. "I didn't really feel like I served my country in the same sense that my brother did. He did a long tour in Iraq. I feel like it is a brotherly competition that he did more than I did, so I want to go back and finish my tour and see my guys through their deployment. It's a bad area and a lot of people were getting injured. I want to be there to help my guys."

If you are looking for McIntosh this week, he's the guy with the American flag and the bald eagle on his prosthesis -- and a Purple Heart.