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Pat O'Connor loved baseball so much he just had to have his own Fenway Park.

So he built one.

O'Connor focused on the important stuff: the right shade of green for his miniature Green Monster, a Citgo sign to sit just past the left-field wall, baseball-shaped markers in right field to represent the retired jersey numbers of Ted Williams and other Red Sox greats.

His attention to detail paid off — for the backyard paradise he calls "Little Fenway," for hundreds of Wiffle Ball players who get to play in it for one weekend every August and for a paralyzed hockey player whose charity is its main beneficiary.

"It started with just planting a seed, and it grew into something a lot bigger than I ever imagined," said O'Connor. "Each year, it seems to get better and better."

O'Connor, a 55-year-old IBM manager and father of three, calls himself "a crazy baseball fan." It's no coincidence he's one of a baseball team-sized family of nine children, or that his e-mail address starts with "homerunpat." He's been in love with the game since he was 7.

You can guess his favorite movie: "Field of Dreams," the 1989 Kevin Costner film about an Iowa farmer who builds a baseball diamond in his cornfield after hearing voices.

In 2001, he built Little Fenway on little more than a whim, turning a one-acre parcel behind his house on a dirt road into a replica of Fenway Park, complete with bases, bleachers, an old-fashioned Fenway-style scoreboard, a 12.5-foot-tall Green Monster and a 3-by-3-foot plastic Citgo sign — it's not neon — that looks a lot like the one towering over Kenmore Square.

And of course, there's the left-field foul pole — "the Fisk pole" — and the right-field foul pole — "the Pesky pole" — so named for famous home runs by former Red Sox catcher Carlton Fisk and shortstop Johnny Pesky, just like at Fenway.

Little Fenway even has tomato plants in the bullpen, a nod to former Boston pitching coach John Cumberland, who in the 1990s planted tomato plants in the Fenway Park bullpen and had idle pitchers tend them.

All the groundskeeping and organizing means O'Connor isn't exactly an all-star when it comes to pitching in around the house. That's OK with his wife, Beth. She's proud of what O'Connor has done. She just doesn't get the same thrill about the sports stuff.

"I don't really get it. I'm not really a sports person, so I don't have that same feeling that I see other people get when they're coming and see how much fun they're having and watch the magic," she said.

What started as a lark became something more after Sept. 11, 2001. O'Connor hosted a Wiffle Ball tournament to raise money for New York disaster relief after the World Trade Center attacks. It brought in $1,400.

That winter, he picked up "Eleven Seconds," E.M. Swift's book about former Boston University hockey player Travis Roy, who was paralyzed from the neck down while playing in his first collegiate game in 1995.

O'Connor had an idea for a charity tournament, and pitched it to the Travis Roy Foundation, a charity that raises money for victims of spinal cord injuries.

In 2002, seven teams played in the first tournament, raising $4,000. Since then, the three-day event has steadily grown — in participants, money raised for Roy's foundation and stature. In addition to the $500 entry fee for teams, the players compete with one another to raise money that they then bring to the tournament.

There's a 20-20 club — for anyone who raises 20 pledges of $20 or more — and a 30-30 club, the members of which are announced in a ceremony on the field each year. Former Red Sox players have found their way there to play, including Bernie Carbo and Bill "Spaceman" Lee.

There's a waiting list for teams to play.

Demand was so great that O'Connor went a step further in 2007, building "Little Wrigley" — a replica of Chicago's Wrigley Field — behind Little Fenway. It has a field and bases, an ivy-adorned faux brick wall, flagpole pennants bearing the names of famous Cubs and a clock that's set to one hour behind the one at Little Fenway — an accommodation for central time, of course.

The two parks swarm with players for one weekend a year, with games running all day and into the night, illuminated by portable lights brought in for the occasion.

"Playing there is the highlight of everybody's summer," said Mario Fontana, 27, of Allston, Mass., who hit a walk-off home run in the championship game of the inaugural Travis Roy Foundation Tournament and hasn't missed once since.

"It's amazing. When you first play at Little Fenway, you aren't prepared for the experience, even if you've seen it from afar. It's constant giddiness. You keep giggling about how fun it is. You can't believe you're getting to do it."

To date, the tournaments have raised $715,000 for the Travis Roy Foundation, and thousands more has been raised with tournaments benefiting other charities.

On Friday, 25 teams will converge on O'Connor's backyard for the ninth annual Travis Roy Foundation Tournament.

The 35-year-old Roy will be there, as he always is.

"It's a magical place that really removes you from everything else that's going on in your life," Roy says. "It just really is a unique setting and a unique place."