Barcelona was dominating Arsenal in the first leg of the Champions League quarterfinal, taking a 2-0 away lead that could have been more. Then the game changed.

Why? What made that game change? What makes any game change?

I asked a couple of people who are in far better position than I am to know such things.

Houston coach Dominic Kinnear saw some tactical changes:

“Two things happened that changed the game. One was Arsenal’s decision to play three at the back. The other was the insertion of Theo Walcott. Walcott’s pace to get in behind (the Barcelona defense) was huge.”

U.S. women’s veteran Brandi Chastain went with another angle:

“When the other team seems to be in control but is not putting away chances, you start to think, ‘Maybe we’re in this.’ And they start to become frustrated with the lack of finishing. Barcelona probably could’ve scored another two goals. That becomes frustration, and then you start to let down your mental guard. Then the other team gets a little bit of success, whether it’s possession or chances on goal.”

Matt Besler from the Kansas City Wizards figures Arsenal just had to turn it up a few notches:

“I think it was just the situation that Arsenal was in. The urgency that they had once they went down 2-0, they knew that being at home that they needed a tie or win, they really needed to go for the goal. I think that was the tipping point that helped them get some more energy and get more urgent. That’s why soccer is such a tough game. You can dominate a game for 70 or 80 minutes, but if you lose concentration for 10 minutes you can lose everything that you worked for.”

Of course, none of these are mutually exclusive. And don’t read into gender stereotypes with Chastain stressing the emotional side and Kinnear going with the analytical side. Kinnear sees several ways a game can change — emotion, substitution, a formation change, even a ref’s decision. And he has seen a team’s mindset change with one kick:

“Even a bad pass can change momentum. In MLS Cup 2006, in the first 20 minutes, we were all over New England. We had one bad pass that gave them possession in our end. That creates a little bit of momentum. They didn’t necessarily get a good chance on goal, but they got a lift.”

That game stayed scoreless through regulation. In overtime, Taylor Twellman got the Revolution on the board, but Brian Ching answered a minute later to send the game to penalty kicks, where Kinnear’s Dynamo won.

The Dynamo’s quick rebound leads to another Kinnear point:

“Whoever said 2-0 is the most dangerous lead is so full of (it). I’ll tell you what, before the game starts, I’ll give you two options: You can either start the game winning 1-0 or 2-0, which would you take? I’d take 2-0. You’re allowed one mistake and you’re still winning.”

If you want to change a game, you have to be adept at overcoming mistakes in the first place. Chastain and the U.S. women had to rally twice in the 1999 World Cup quarterfinal, first giving up an own goal when Chastain put a backpass past Briana Scurry. The USA answered, but Germany made it 2-1 before halftime. The 1999 final victory (and the ensuing national discussion of Chastain’s bra) wouldn’t have happened without a comeback by a team with supreme faith in its mental game.

“With the women’s national team, we were going to put the other team under pressure and suffocate them mentally,” Chastain says. “When things weren’t going well, that’s the way we changed things for us. With that team, the majority of it was mental. The will of a team can be very strong.”

Yet that will can be disrupted. Chastain points to the most controversial coaching move in U.S. women’s history — Greg Ryan’s decision to replace goalkeeper Hope Solo with Briana Scurry to face Brazil in the 2007 World Cup.

“I can’t tell you how many times I’ve heard, “Oh, it wasn’t our normal lineup. We were thrown off mentally.” Those things can disrupt – they shouldn’t, because all the players are capable of playing. Those kinds of changes can really interrupt some players and their ability to do what they do on a regular basis.”

Chastain hasn’t committed to a career path since the WPS’ FC Gold Pride released her in the offseason, but she sounds very much like a future coach.

“The emotional side of the game is underappreciated, and it’s not worked on as much as the physical side.”

NHL players know how to shake up the emotional side of the game. They go out and get a big hit, sometimes dropping the gloves and fighting. Soccer players get way more than five minutes in a penalty box for fighting, but a physical challenge can change a game, Kinnear says:

“I look at Toluca vs. the Columbus Crew, the first game where Toluca was cruising 2-0. There was a big physical confrontation. From that point on, Columbus took over the game. Toluca lost their composure, and Columbus got good energy out of that.”

In the second leg, Arsenal was the team getting on the board first, thanks in part to the dangerous Walcott. Then Barcelona stormed back with four goals, all from Lionel Messi.

If you have Messi, you know your first option for changing a game. Everyone else needs to try something else. (As we saw today, a red card and a screamer from Arjen Robben can help as well.)

Correction: The original version of this post incorrectly stated the year of Greg Ryan’s decision to replace Solo with Scurry. I had talked a bit with Chastain about the 2003 World Cup game against Germany in which the USA did NOT make a needed tactical adjustment, hammering aerial balls into the box over and over again even though Germany’s defense was perhaps the one defense in the world that could handle such threats. So naturally, I confused 2003 with 2007. Yes, it will be the policy here to point out corrections and explain why, even if it’s a misfire of the brain like this one.