Brief Answer:
Please give details.

Detailed Answer:
Hi.
Thanks for your query, albeit small and specific.
The most probable reasons for a small ball under the ball sac (scrotum) between the legs are:
- Sebaceous cyst or a Boil; depends upon the duration of the swelling.
- Lipoma.
- Can be anything which needs clinical evaluation and actual physical examination by a General Surgeon. Investigations to confirm the clinical diagnosis.
- Can be due to a sinus or fistula formation.

Please give me more information so that I can help you more:
- Since when have you got this swelling (duration) ?
- Is there pain / redness or tenderness ?
- Is the size constant or increasing ?
- Is there any symptoms related to urination or passing stool ?
- Please mention any other symptoms which you think may be related or not related to this problem,; this may add to my knowledge.

I hope this answer helps you. Please feel free to give the feedback, ask for further relevant queries or if you feel that there is a gap-of-communication.

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Brief Answer:
Get a diagnosis and get operated if advised so.

Detailed Answer:
Thanks for your feedback.
This is most probably a cyst then.
An examination by a General Surgeon will certainly help in the proper diagnosis and plan for a treatment. Due to the site of the swelling, i would strongly advise you to consult a General Surgeon and get a proper diagnosis and a plan for Surgery.

I hope this answer helps you.
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