Question

Why do you think that sports-related injuries are more likely for kids who specialize in one sport, 

Answer 1

Answer:

Because they don't use a variety of muscles as much as they could by doing more sports so when they use the lesser used muscles, they could get hurt.

Explanation:    

Answer 2

Because they are not always working as many muscle as they would when playing many sorts such as playing cross country where you run with your legs then playing baseball where you work your arms