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.”