I grew up with four siblings who were all into sports and now I have kids who are into sports at school. I can pretty much tell what's causing calf and ankle pain from my experience.
If there is tenderness and swelling along with the pain, it's definitely an injury or a strain. If there is no swelling but the pain is constant and doesn't go away with rest, then it's probably a foot problem.
My grandmother has arthritis related ankle and knee pain that resonates to the calf, so that's another cause in older people.