It can happen in the blink of an eye, and the effects can last a lifetime.

11 Sports captured on video two girls colliding heads during a soccer game—one of them suffered a concussion and didn’t even remember the incident. It’s a dangerous situation for any young athlete—and a serious scare for parents.

The family of Caitlyn Troupe contacted 11 News and asked to see the video. Sports director Jesse Kurtz slowed the video down to help the family see how the concussion happened. What they saw revealed a situation that any athlete could find themselves in at any times, making concussions such a scary issue.

March 29, 2011: It’s a day that changed the way Caitlyn Troupe played the game of soccer.

“We got a free kick, lined up at the 18-yard line. As soon as it came in, I don’t remember anything like that,” Caitlyn told 11 News.

Caitlyn scored the game-tying goal, but has no memory of the moment.

“I remember waking up with teammates around me, “ Caitlyn said. “Couldn’t remember what happened, or who passed the ball. Don’t remember, scary.”

Coaches, trainers and an on-site EMT helped her off the field. She was taken directly to the emergency room, where she was diagnosed with a concussion.

Caitlyn’s mother told 11 News that Caitlyn’s behavior after the collision indicated that something was wrong.

“I knew she wasn’t acting like herself. She’s quiet, but not spacey. She was slow to answer. She was crying.”

Caitlyn's injury is more common than you might think. In fact, girls’ soccer is second only to football in the frequency of concussions during play in the nation.

“Caitlyn is the third on her team, four this season,” Caitlyn’s mother said.

Doctor Jack Sharon of Penrose-St. Francis Hospital has seen a surge in this growing problem

“Most of the concussions are sports-related,” Sharon said.

Sharon urges players and parents to pay attention to the following symptoms after a head collision: headache, nausea, vomiting, blurry vision and/or an inability to think clearly. These all may be indications of a concussion.

“If those symptoms persist for any length of time, or reoccur for hours or days after injury, those are reasons to get checked out,” Sharon said.

It's also equally important to stay off the field for at least a week after symptoms subside

“You don’t go back until you’re 100 percent normal. Normal at rest, normal going slowly through practice,” Sharon said. He said that the second concussion can be worse than the first.

Caitlyn Troupe missed two weeks of games.

“It’s so hard sitting on the bench when you could be playing, but it’s worth it,” Caitlyn said.

She now plays with protective head gear. So do a handful of her teammates, to minimize the risk of another concussion, which Caitlyn now knows could carry permanent consequences.

“You could have brain damage, or injure yourself,” Caitlyn said.

Caitlyn plans on scoring more goals in her soccer career. And thanks to a lesson learned, she'll remember each and every moment. One moment she’ll never forget: scoring the game-winning goal Wednesday night, lifting the Titans to the 3A state championship. Caitlyn returned to her team about mid-season.

Just this year, Colorado Governor John Hickenlooper signed a bill into law, requiring that all youth coaches receive more training in recognizing concussion symptoms. It covers coaches in public and private schools, as well as volunteer coaches. The training is free, and is done online.