They are like two chess masters who've sat eye-to-eye at the board for years, and yet still are figuring out each other's every strategic nuance. Even after all this time, there's something, however small, to pick up on and react to. And so they keep bringing out the best in each other.
North Carolina coach Karen Shelton is in her 30th season leading the Tar Heels' field hockey program. Her counterpart at Maryland, Missy Meharg, is now in her 23rd season. Shelton is two victories away from 500 in her career; Meharg got win No. 400 earlier this month. They are both former U.S. national team players; Shelton won an Olympic bronze in the 1984 Los Angeles Games.
The Tar Heels have six NCAA titles, all under Shelton. The Terps also have six; five since Meharg took over the program in 1988. Only Old Dominion, with nine, has won more NCAA championships in this sport.
North Carolina and Maryland have been particularly dominant since 2005: One or the other has won the past five national championships.
Shelton and Meharg have met for the NCAA title three times, including last season when the Tar Heels scored on a penalty corner with 11.7 seconds left for a 3-2 victory.
And this weekend, No. 1 North Carolina, 16-0, and No. 2 Maryland, 15-1, play in the marquee regular-season matchup in field hockey, meeting in College Park, Md., on Saturday. Both are 9-0 in the ACC.
"It's just a thrill for a Division I athlete to have this kind of game in the regular season," Shelton said. "So we're eager to experience the excitement, and have the opportunity to play our best under hostile conditions. We played [No. 4] UConn at a neutral site, and [No. 3] Virginia at home. So we haven't had a big game on the road.
"And we know that this perhaps might be a game particularly targeted by Maryland. Obviously, their returning kids, after last year's national championship, will give us a special effort on Saturday."
The Tar Heels and Terrapins play this weekend on the same University of Maryland field where they could meet again in November for the NCAA title. Plus, there's a good chance they could face off for the ACC tournament title early next month in Winston-Salem, N.C.
"We have quite a history of that," Meharg said of playing three times in a season, with each meeting having increasingly higher stakes. "It's always such a wonderful battle, very respectful.
"In [Saturday's] match, the outcome isn't as important as what you learn to take into the postseason. Each of us is watching how the other presses, how we bring the ball out, what defenders we put on people. You might do something different in this game than you would if you meet again. I enjoy the tactical challenge."
Considering how long these coaches have been rivals in the same league -- going head-to-head not just on the field, but in scouring the same areas of the country for the top players -- it would be understandable if they'd developed some ire for one another. Or at least would trade some heated words or caustic comments.
But that hasn't happened.
"I really believe that if it weren't for North Carolina field hockey and the strength of the ACC, I'm not sure as a young coach I would have had the markers so clearly identified for what I needed to do to win," Meharg said. "Karen is a fierce competitor, and in many ways she taught me how to do that. I got our definition of tradition in part by going against theirs. Both programs have a distinct way to compete. They're a first-class program, and I'm proud to be aligned with them in our sport. We both want to win, of course, but there's always a gracious respect, win or lose."
Or as Tar Heels sophomore standout Kelsey Kolojejchick puts it colorfully, "It's a great competition and rivalry -- it's not like a vicious, bloodbath type of thing."
Kolojejchick -- it's pronounced Ko-lo-jay-chek, but she's fine with people just saying Kelsey K -- had an outstanding 2009 season, being named national and ACC rookie of the year. She was the first Tar Heels freshman to be a first-team All-American.
Her older brother Matt -- nicknamed Kolo -- plays on the UNC football team. The siblings are from field hockey and football territory: the Wyoming Valley in northwestern Pennsylvania, near Wilkes-Barre.
Kolojejchick leads the Tar Heels with 14 goals and six assists, and she's been particularly important in the absence of senior Katelyn Falgowski, who's been out all season after suffering a concussion.
The Terps' top scorer is senior Katie O'Donnell, last season's Honda Award winner as the nation's top player. O'Donnell currently has 21 goals and 23 assists, and she's from Blue Bell, Pa., in the southeastern part of the state.
Shelton grew up in an Army family that settled in Pennsylvania when she was in fifth grade. Meharg is from Chadds Ford, Pa. So both coaches and their current respective stars are from the heart of field hockey country.
"Field hockey was actually the first organized sport I played," Shelton said. "I grew up playing whatever my four brothers played, but in the seventh grade, I tried out for the field hockey team. And I loved it from the very first day."
Both she and Meharg still sound just that enthusiastic. And that's the energy they and their teams will bring into a match Saturday that could be a preview of an even bigger one we could see a month from now.
Top matchups this weekend
" Volleyball: Cal has been frustrated more often than not in its rivalry (or lack thereof) with Stanford. The Cardinal, six-time NCAA champions, lead the series with the Bears 62-8. But last season, the teams split their two meetings. And on Friday night, Cal, ranked No. 5, visits No. 2 Stanford with first place in the Pac-10 on the line. Both teams are 7-1 in league play.
" Men's soccer: It's a meeting between two middle-of-the-pack ACC teams … but they're still both ranked in the top 25. Virginia, which is No. 8, travels to No. 20 Boston College for a Friday match. Saturday, No. 1 Akron faces the second-place team in the Mid-American Conference, Western Michigan. The Zips are coming off a 7-1 demolition of Michigan on Tuesday. By the way, another Big Ten team has kept Akron, 12-0-1, from being "perfect" this season: Ohio State, which tied the Zips 2-2 on Sept. 29.
" Women's soccer: There are three key conference showdowns Sunday, with all six teams involved ranked in the top 11. First off in the ACC, league leader North Carolina, which is ranked No. 3, hosts No. 6 Maryland. Later, the top two teams in the Big 12 square off as No. 5 Oklahoma State travels to No. 7 Texas A&M. The Cowgirls enter the weekend at 14-1-1 overall and 7-0 in conference, while the Aggies are 13-3 and 6-1. Oklahoma State faces Texas on Friday, while Texas A&M plays Oklahoma. And in a match televised by ESPNU at 3 p.m. ET, No. 2 Portland meets No. 11 Santa Clara in the West Coast Conference. The Pilots and Broncos go into their matches Friday -- when Santa Clara meets Gonzaga and Portland plays San Diego -- tied atop the league at 3-0-0.
Mechelle Voepel is a columnist for ESPN.com. She can be reached at firstname.lastname@example.org.