Pain in the upper left abdomen and chest area can be due to stomach issues, spleen issues, due to an abscess below the left diaphragm, a hematoma (localized collection of blood), an
abscess, or a muscle pull (as it happened while playing). Ultrasound would have ruled out
spleen problems and an abscess below the left diaphragm. A CT scan would be more diagnostic.
The chances of it being a muscle pull are very high. It could also be an abscess or infection in the skin or muscle layer.