During my softball game I was rounding first base and felt a pop in my calf. The pain is still intense and I can't flex or bear weight on it. What2 do?

Seek treatment. This is likely a gastrocnemius (outer calf muscle) tear which despite significant pain heals well without surgery or treatment. This should be seen to make sure it is not an achilles rupture. Visit www.Aofas.Org to find an orthopaedic foot and ankle specialist.
Achilles. Good chance you strained or tore your achilles tendon. See a physician now. You need an exam and probable imaging studies. It may require casting or surgery. The longer you wait, the greater the chance of a less then favorable outcome.