Just because old people tend to break their hips more often than younger people wouldn't necessarily make soccer anti-correlated with hip injuries. In your exa

Just because old people tend to break their hips more often than younger people wouldn't necessarily make soccer anti-correlated with hip injuries. In your example, if you compared two groups that are identical, the only difference being one plays soccer and the other doesn't, you'd find a correlation between soccer and broken hips.