Olive sized lump in groin noticed after a workout that eventually went away. it was under the skin and was not painful. any thoughts what it could be?

Hernia?: Inguinal, or groin, hernias are holes in the abdominal wall through which abdominal contents such as fat or intestines can protrude. And appears as a lump under the skin. If and when the contents return to the abdominal cavity, the lump disappears. May it may not cause pain. You should get an exam by your primary care at the next available time on find out. Hope this helps!