If you are someone who is worried about your teenager getting hurt during an after school sport (such as a concussion) then you are probably a bit hesitant about them getting involved in full contact sports, and perhaps even other sports such as basketball, where there is still the chance of getting knocked about. But if your teenager is not the type who is content with drama club, or chess club, or something else that is less physically demanding, then you are going to want to learn about sports that are still going to give them the chance to be active without putting them at risk for a concussion or something else.
Classical Ballet Class
Dance is one of the most energetic and fun exercises. While it's not technically a sport, it can easily be a fun after school alternative for your teenager. Ballet for teens not only looks beautiful, but it is a fantastic way to get into shape. You wont risk the same injuries that you would playing a sport such as football, hockey, or even basketball, but you do get the great physical benefits. What you do get, in addition to a really great workout, is a fun class where your teenager will get to experience art and culture and have the chance to develop a beautiful skill.
Track and Field
If you're teenager is into running and likes the idea of racing other kids, then you should look into track and field. It's a fantastic team sport (relay races, etc..) without the serious chance of injury. There are even events such as hurdles, and long jump. The cool thing about these track and field events is that your teenager can go with their team to track events and compete at outdoor events (especially if they also run cross country). It's a fun and health alternative to full contact sports.
The lowest of low impact. It's simply one of the best choices for people who don't want to risk injuries. The pool is a great place for people to have fun and exercise. Your teenager can either swim speed sprints, or do long laps. It's a team sport, which makes it great for teenagers who don't want to practice something solitary and would love to be part of team effort. If their school does not have a pool, then you can have them join a local gym that has a pool. There are intramural swimming teams that they can join and be part of.